right let me clarify. I know that the itc files in the download folder carry a persistent id, however, that id is not the track id like it is with the local folder and the xml file contains only track and library ids no album id. unless i am wrong, in which case i have to ask where in the xml/wherever else you are finding the album id?
as for extracting the art if you read the itc file from byte 492 to eof that is the image data 90% of the time. you can parse the itc file if you want to be precise. you can play around with it using a hex editor. simply delete the header off the file (header end with the ascii string:locl, if i remember right) and rename it with the proper image extension (either jpg or png depending on the data) and preview will open it just fine.
my advice on how to move forward would be different depending on how you are constructing you music library. if you use the itunes.xml file exclusively or if you simply drill down through the itunes music folder. if you are building off the xml file you can just use the "track persistent id" (for local folder only) to find the proper itc file and display the image data. this will prevent your users from having to do "imports".
of course if you are simply drilling down through the folder hierarchy I would suggest simply reading the embedded art in the files ID3/atom tag. I can help you with how to do that as well since that is how NBB did things in the beginning.
I find that ALOT of people ***** about FEs not being able to display the art downloaded through the itunes download album art function, however.
since those downloaded that way are only stored as itc files in the "download" folder your only hope would be to decipher the way apple generates persistent ids or if AIR can somehow use quick look but that is mac only
regardless I really don't have AIR exp so my advice may be shaky