Google Images is a good resource for images. Though it is too broad i.e. not so specific.

There are some works especially in the field of health information, studies related to how midics search for and use medical images or videos. See for example works by Shahram Sedghi

http://scholar.google.com/citations?user=JzJ6xQUAAAAJ&hl=en&oi=sra

and works cited in his works. 

That is awesome! Thanks so much! I have a fairly extensive library on medical image perception, but very little of it looks at semantic meaning and information.