The following is just some technical drivel that you may want to ignore.
Using Google to search for images, I realized that there are privacy issues caused by naming conventions. For example if I name an image with a name that refers to that image, it can be searched by anyone online that types in that keyword. So a descriptive name such as "lunchinthepark02.gif" can be found by typing in lunch, or park or 02.
The next concern is how are these images used? Certainly they can be republished without much regard for ownership. In the case that you would not want your images used in this search manner, the naming convention "image01.gif" does not exactly describe your image, but it makes it almost impossible to filter by subject.
Applications such as Adobe Imageready have the default set to name sliced images...image01, 02, 03, etc. This software slices up a large image into columns and rows for HTML tables. Changing each image name using this application would not make sense...unless the images were all renamed before being linked to by a web page and after Imageready creates the new sliced up images. Extra work that might just open up that copyrighted image for your client to anyone who knows how to use a search engine.