Did you try the Raspian OS yet?
Look at ImageMagick, curl and wget.
I am new to Linux in general, but I have been using Ubuntu for a signage project. I want to start using the raspberry but have a couple of problems. One element of the signage is slideshow, in ubuntu i have been using wallch to achive this but i cant find a suitable way to do this on the Raspberry. The reason i am doing it this way is the other element of the signage is a pdf that has to live over top of the changing background. This pdf is housed on a server and has to be updated daily. I will use any OS distro availible that you guys might see fit to use, right now i have one loaded with Fedora Remix 14 and one with the stock Dabian SD card that came with it. Thanks for any help that you can offer...