Is there a master index of all the images available in the Wizards of the Coast Art Gallery files? When I want to find a specific image, I have to open the file for each individual issue of Dragon/Dungeon magazine. The WotC search tool doesn't appear to index the images in the Art Gallery files. Neither does Google because the files are behind the DDI paywall. I would like to just search an index that tells me what Dungeon/Dragon issue contains the image and then I can just open the one file from the Art Gallery Archive for that issue. Am I'm missing something?
Sadly, there is no public tool or list that has this information. Now if someone has a passion for this and nearly infinite time then they could start one...
You might try sending a customer service email to WotC and see if they have something. This may be your best bet.
I don't know if this is what you're looking for as 4th edition is before my time but by doing a Web Google search on the domain archive.wizards.com you might be able to get some results as it looks like all the images are up on the site and the pages themselves were not marked no-index (only the images).
There's also the DM's Guild which has art assets for people making content for the DM's Guild. I don't know what you're trying to do with the art, but you might be able to use them if you're not going to distribute it outside of the DM's Guild.