I think it is false advertising and geneivas daas to photo shop ANY advertisements or appeals for tzeddaka. To clarify on some of the points mentioned above:
1. If the yeshiva usually looks one way (completely full), but on that day that the picture was taken a large number of boys were out sick, then perhaps it would be ok.
2. Was the boy who’s shirt was changed color a student at the institution or a guest?
3. Adding nature and greenery to the surroundings is problematic. It can show that the money collected goes towards trees and flowers. On the other hand, many people like knowing that the institution has pride in themselves and their institution and might want to give more towards it than usual. But, if it isnt…..
4. At weddings, the photographs are many times enhanced, blemishes taken away ect. These pictures are not for public displays or announcements so there would be no genaivas daas involved, to the best of my knowledge.If it was a photographer trying to show how well he takes pictures, then that would be different. Computers arent the same as talents. For institutions to make the picture clearer or make it look a little sharper it might be different.
Basically, the institution should be very carefully walking the fine line between natural enhancements and gineivas daas. Why dont they just tell the photographer to come back another day?