Name your images in a way that describes what they are. Don't get carried away though. If it's a picture of a purple widget, name it purple-widget.jpg, rather than leaving it whatever your camera or photo editing software wants to name it.

Hello,
An often overlooked part of WordPress SEO is how you handle your images. By doing stuff like writing good alt tags for images and thinking of how you name the files, you can get yourself a bit of extra traffic from the different image search engines.
Thanks.

It is always better to label the image by changing its alt tag to the most relevant keywords for maximum benefit than to leave a default name or the serial number of the image that the camera gave it.