Tip: A quick way to get to the Themes folder is to go to:
Options > Theatre View > Appearance > Theme: {name of current theme} > Browse themes folder...
I have a few Themes I use, currently Dakar images. They play in the background in most areas of MC, even while Audio is playing if there are no more appropriate images. For example, if I don't have "Last.fm" ticked under the "Online media slideshow" and play some audio, my Dakar theme shows in the background behind the Album Cover Art. But if I tick "Last.fm" under the "Online media slideshow" and play some audio, the Cover Art shows over Artist images in the background for a while, and then the Cover Art disappears and only the Artist images from Last.fm are shown.
However, my understanding of your question is that you have multiple images for albums that are stored in the Album directory, and you wish to display these when an Album is played, correct? This has been asked for before, but I don't know of any way to do it yet.
JRiver have provided some capability in the View Extras functionality, but it doesn't do what you want. Right click on an audio file in Standard View. Select "View Extras" at the bottom of the list of functions, and select the first image in the list shown. Then select Play and the images in the Album folder, or those supported by the View Extras functionality, will be shown on screen. Just once I think though. No repeat I know of.
Search the forum for discussion on "View Extras" or "Extras" for more info.
But wait... Now I think about it, at least one user has worked out how to play a slideshow of his personal images while audio is playing. From memory it was just generic images he took as part of his photography hobby, and it involved the use of two Zones, one for audio, one for video, both played at the same time. I'm not sure how automated it was though. You may be able to do a similar thing and direct MC to the Album directory for the source of images.
If you search the forum carefully you may find the discussion. Using Google to search the JRiver domain would work best.