Photo's from both WDW and DL will work. . . they don't care. I asked and checked and many people have done pictures for both, so if you still want in you are welcome. Just let me know.
Yes, they do combine. I just shared with someone and she was at WDW and I was at DL.
I can't stress this enough...you cannot view your pictures under any other user-name or account. If you all know the user info. beforehand, it shouldn't be an isue at all, but we had four people who were going to go together for this and then it got messed up because two of them logged in while they were at Disney...didn't realise that was the same thing.
When we were at DLR for three days in March/April, we had 12 pictures taken. They all had three or four backgrounds that you could add, and I went in and applied pretty much them all to each of the pictures. A few I changed the layout from verticle to horizontal and put stuff on. I think I ended up with about 50 pictures at the end. But, since I only had 12, I think I was fairly crazy about it.
At DLR, all the character meeting/greeting has the option and then various backdrops (we got in front of Mickey & train, three different places in DCA, the castle and space mountain. It doesn't include any of the pictures on the rides, nor any of the character meals (a disappointment for us.)