The Gettysburg National Park Commission [The Commission is also referred to as the Gettysburg National Military Park Commission or the Gettysburg Park Commission], established by the United States Department of War, after they took over the administration of the park from the Gettysburg Battlefield Memorial Association (whose funds had expired) on March 3, 1893, and whose stewardship was later transferred to the National Park Service in 1933 (SOURCE), took a pictorial inventory of many of the existing monuments in the eventual historic district (a majority of them seem to have been Pennsylvania monuments being there are over one hundred of them). These pictures were included in their yearly Commission reports. I have found hundreds of these pictures on Virtual Gettysburg, a comprehensive website which pictorially inventories all the monuments and provides minor narratives as well. All the photos look the same as if they were taken by the same camera and in the same approximate time period. Even the angles are all the same, positioning the monument at a slight right angle (standing to the left), revealing a little of the left side of the monument. The entire park looks so young and immature when the photos were taken. After all, the Battle of Gettysburg was thirty-seven years old at the time and war veterans were only in their fifties. I have never been able to find any photo credits (I have a sneaking suspicion some of the photos may have been snapped by members of the Park Commissions and published in their annual November report to the War Department) but I know they are public domain because their copyrights have all expired. This picture represent the efforts of the Commission well into the Commission period. Most of my pictures I use come from a website called Virtual Gettysburg. It seems however, all the pictures of the New York monuments were either borrowed from or shared with a New York monuments website. That site, The New York State Division of Military & Naval Affairs can be found HERE. This picture was on the Virtual Gettysburg site and can be found HERE.
Clearly it is evident, through a survey of historical pictures and other archival information (such as the annual Commission reports), much change has occurred at Gettysburg Battlefield. With the passage of legislation affording historical status to this site as well as placing it under the auspices of the National Park Service, its patrons and caretakers had to groom and prepare the area to make it more authentic as well as educational. Today the battlefield has managed to maintain an authentic 1863 feel, but back then, as evident in the many photos, it was a desolate, empty place of brown and green fields broken only by the occasional farmstead, their outbuildings and fields of crops. With the emergence and dedication of hundreds of monuments during the commemoration period and all the other dedications prior to 1900, and the development of farmland, some change has occurred but for the most part, nothing too dramatic. I believe this monument was taken at the dedication in October of 1889 as the 12-pounder fake Napoleons are nowhere to be seen. They were added in the 1890s according to records. As far as differences in the two pictures, everything with the monument is the same. The cannons of course are missing as is the grass and tall trees in the background. They do otherwise match up nicely.
The 6th Maine Battery Monument is located on the left or west part of Hancock Avenue if traveling north toward the Pennsylvania Monument which looms hugely in the distance. This part of the battlefield is the south section of Cemetery Ridge. The monument is flanked by a couple of 12-pounder Napoleons, which apparently are not Napoleons but 6-pounder Field Guns altered to resemble 12-pounder Napoleons in the 1890s. 
Parking is available at small, cutout shoulders along the road, some wide, some narrow. Be sure to stay off the grass or you will be ticketed by park police. I visited this monument on Thursday, July 5, 2012 at 5:31 P.M. I was at an elevation of 550 feet, ASL. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos. If looking at the front of the monument, you would be looking west, the guns point due west. To match up the picture, I had to face a perfect 45 degree angle or southwest, about 5 feet away.
From a previous waymark about this monument:
The 6th Maine Artillery, Battery F was also known as Dow’s Battery (This is also written on the front of the monument). During the battle of Gettysburg, the unit served as a member of Taft’s Brigade in the Artillery Reserve, Army of the Potomac. The 6th was commanded by Lieutenant Edwin B. Dow (1835-1917), a clerk from Portland. Dow was wounded at Cold Harbor. Under his command were 103 men and 4 Napoleon cannons and among the men, 13 were wounded.
Born in Canada young Edwin Dow
was a 26 year old Portland, Maine
resident when on February 6, 1862
he was commissioned 2nd Lt. in
Freeman McGilvery’s 6th Maine
Battery. He would rise to the rank
of Captain and at Gettysburg his
name would be etched in stone as
commander of Dow’s 6th Maine
Battery. SOURCE
From the Historical Marker Database, Craig Swan: Dow's Battery was Battery F of the 6th Maine Light Artillery. It was commanded by Lieutenant Edwin B. Dow and was part of the 4th Volunteer Brigade, Artillery Reserve. Dow was attached to McGilvery's 1st Volunteer Brigade during most of the battle. Thrown into action on July 2 as the Federal Third Corps withdrew, the battery fought east of the Trostle Farm. Later it relocated on Cemetery Ridge, where it participated in the actions of July 3. The battery brought four 12-pounder Napoleon guns into the battle, and lost none. Eight men of the battery were wounded, and five horses were lost. SOURCE
The Draw the Sword site helped out by the NPS narrative and the SIRIS site offers the following description: Tapered square marker stands on a low, rough-hewn base. A pyramid of cannon balls tops the piece. Relief elements on the front face include a star, cannon barrel, rammer, drum and other military accouterments. Monument is a two-part tapered granite shaft with a top containing five stacked black polished cannon balls and set on a six foot square rough cut base with a tooled edge. The lower part of the shaft has a bas-relief front and the upper part has a bas-relief front, with incised inscriptions on four sides. Flanking markers are 1×1.6 foot. Monument marks the position held by Dow’s Maine Battery on July 3, 1863 from the morning hours until 10:00 A. M. on July 5. They engaged in artillery duel preceding Longstreet’s Assault on the third day.
This monument was dedicated on October 3, 1889 by the State of Maine. The monument is composed of granite and the cannon balls are of polished black Addison granite and the base is of granite. The monument has the following dimensions: approximately 9 feet 8 inches in height and the base is approximately 1 foot 6 inches x 6 feet x 6 feet. I was unable to recover the name of the sculptor who labored on the project. There are the briefest of inscriptions on the front, left and right sides of this monument which read:
(Front):Dow's
6th Maine
Battery
(Left):McGilvery's Brigade.
Reserve Artillery.
(Right):Campaigns A.P.
1862.-1865.
The 6th Maine Battery Monument is a contributing feature to the Gettysburg National Military Park Historic District which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Government, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The original National Register Nomination was approved by the Keeper March 19, 1975. An update to this nomination was approved by the Keeper on January 23, 2004. The monument is identified as structure number MN270-D.
From the Nomination Form:
1 of 15 Civil War Monuments to Maine of the GBMA Era (1863 - 1895). Indicates position held by Dow's Maine Battery morning of Jul 3, 1863 to 10:00AM Jul 5. LF&RF markers 60'&122' S-N, respectively. Mn has 2 flanking markers and 2 cannon. Located W side of S Hancock Avenue.
Short Physical Description:
Mn w/2 flanking markers and 2 cannon mounted on cast iron carriages. Base 6'sq x 1'6"H rough cut, tooled edge. 2 part tapered shaft, 1st bas-relief front, 2nd bas-relief front, incise inscriptions 4 sides. Top, 5 stacked cannon balls, black polished. LF & RF 1'x1'6"x1'10", chipped.
Long Physical Description:
Monument that has two flanking markers and two flanking bronze Napoleon cannon mounted on cast iron carriages. Monument is a two-part tapered granite shaft with a top containing five stacked black polished cannon balls and set on a six foot square rough cut base with a tooled edge. The lower part of the shaft has a bas-relief front and the upper part has a bas-relief front, with incised inscriptions on four sides. Flanking markers are 1x1.6 foot. Located on the west side of south Hancock Avenue.
My Sources
1.
NRHP Nomination Form
2.
SIRIS
3.
Stone Sentinels
4.
Virtual Gettysburg
5.
Draw the Sword
6.
Historical Marker Database