all my images are named based on the item # so they look like DC023.jpg. However all images do have correct alt tags. Is it worth whiel to rename all images to better reflect what the image is off? also what about all the images that are currently indexed?
should i leave a set with old names on the server?

thank you

name the pics

when i rename and replace all the images, is it safe to delete the old ones from the server or no harm in leaving them?

thanks

Put in 301 redirects from the old to the new.

how do u do a 301 on an image?

In its simplest form the same as for any file:

Redirect 301 /filepath/oldimage.jpg http://www.example.com/filepath/newimage.jpg

name the pics using your keyword that is relevant to your site.

To prove a point here, do an image search for what you're looking for. E.g. "Fir tree". So the search URL is: http://images.google.co.uk/images?sourceid=chrome&ie=UTF-8&q=fir%20tree&um=1&sa=N&tab=wi&safe=active

Now look at all the results - the top searches don't have an ALT tag on the image result in the article. Their file names (or at least, the entire URL) do.

So that goes to prove the theory!