Hi All,
Sorry if I am replying late on this thread, but just found it.
I have good results on google image search for most of my images, and therfore a lot of my traffic comes from these image searches.
Make sure you ALT tags are using keywords within them, dont just name them "robot t-shirt" as you will be competing with thousands of others. ALT tags along the lines of "organic cotton t-shirt depicting an image of the 80's robot with a flower on its head" will bring more traffic from the "long search strings". This will also bring you highly targeted traffic, more likely to buy.
The t-shirt file name is also very important, a file name of xxxx-robot.jpg will again bring you nothing, due to high competition. A file name of organic-cotton-t-shirt-robot-flower" would be more specific and google seems to like these when they relate directly to your site and also to your ALT tags.
The next thing to consider, and this goes against all website design rules, is that google rates (or did rate unless the mayday update has changed it) the size of the image aswell as the ALT and file names. Images with similar file names and ALT tags will be ordered in size first. The larger rating higher on results. However, be very careful as the rule of thumb of website design is to compress your images for speed first.
I hope this helps, I managed to get most of this information for free from an SEO who happens to be staying with me at the moment!, my site rates well on google images, for my specific keywords, but as with all free information please dont shoot the messenger if any of this information is wrong!
mark
Green clothing, Organic Cotton T-shirts and fairtrade t shirts, all by nosymbolrequired