I just came over from the PC side (and wonder why it took me so long). Specs on 27" iMac are 3.4 i7, 16gigs ram, ATI 2 gig vram, 256 SSD internal, 3TB external firewire drive, 1TB external USB drive and a 500 Gig external usb drive for Time Machine. I store my photos on the 3TB drive and have tried to use some of them as wallpaper. I went through the menu in the "Change desktop backround" app. Went to the bottom and clicked the "+" sign and added the proper directory. The photo I chose shows up in the box and desktop is set to that photo....until I reboot! Then is comes up with the Galaxy wallpaper even though the one I chose is still shown it the "desktop" app. Can anyone help me?