Aaron makes a good summary of the factors to consider when optimising images in Google image search.
The text surrounding the image does seem to be important. Searching on my name brings up a couple of web page elements which backs up this theory. Clever naming of the filename though seems to be the simplest way of approaching this. No more img20045.jpg files – get the hyphenated product name in there (and preferably the brand).
We’ve done this for several shops clients and it brings in 15-25% traffic increase. People like to shop visually, especially with luxury, high cost items. Another reason for making sure your e-commerce images are high quality shots in the first place.
The downside is the time, it’s not easy renaming thousands of files but sometimes you can cut some corners using the free batch rename tool in Ifranview.