Try Public Service Announcements on local radio and tv/cable stations. They are free. Also see if your local paper would be willing to feature an "Adoptable Pet of the Week" with a picture and also if they would run a story on the plight of the shelter and the need for funds, donations and volunteers. Those are a few things that might help get the word out to the public, of course only if the shelter is willing to go that route.

I think your idea for helping with pictures is great. Getting them set up on Petfinders with good pictures and descriptions might really help the adoption rate.