I have a site with several thousand of images. All those images included into the sitemap submitted to Google Webmaster Tools. The amount of 'submitted' images is OK, but the amount of 'indexed' is significantly lower than the amount of 'submitted' and it is going DOWN!
I'd understand if not all of my images got indexed (however it is also not clear and very frustrating for me) but I can not understand how the indexing can go in the negative direction?!
All the images stays on their places. And pages containing them stays unchanged. At least they intended to be.