Since many of the resources on the Fold3 site seem to have come from the National Archives, it only makes sense to stop over at their site to see what they offer. They have uploaded many of their Civil War photo collection to Flickr – you can find it here: National Archives Civil War Collection on Flickr. The agency also has over 200 photos listed at this link: Pictures of the Civil War.
The Library of Congress has a considerable collection of records related to our nation's history. So it is always one of the first sites I visit when looking for photos or maps for research. And because much of the material is no longer under copyright, you can use it for illustrating a story or other work. But before doing so, make sure to check any copyright information listed for that item. You can find Civil War maps here: Library of Congress Civil War Map Collection
The Civil War Trust website now has an animated video and map with a narration of the entire battle. You can watch and listen to it here: Gettysburg Animated Map. The site also offers video narrations of other Civil War battles.
Another favorite site of mine for historical maps is the David Rumsey Historical Map Collection site. Here you can find numerous historical maps from all over the world. The maps related to Gettysburg are at this link: Gettysburg Battle Maps. Fortunately the site offers the maps through a Creative Commons license that allows the material to be reproduced and transmitted as long as it is not for commercial use. There is also an option to embed maps on your own website as shown below.
Modern Day Gettysburg
Finally, for those of you who are looking for photos of the modern day Gettysburg Battlefield, I have uploaded several I took on a recent visit. I also have posted them with a Creative Commons license that would allow you to use them as long as it is not for a commercial purpose. You can find the set here: Public Works Group Gettysburg Photos