There is no formal queue, it's a kinda sloppy system. Here's how it works.
You, the users, upload covers you think meet the requirements to be uploaded to TCP.
Some crazy admin actually doing his job (not me

) downloads the file and temporarily deletes the cover from the queue so that another admin doesn't try to upload it again (which would result in a dupe cover)
If it doesn't pass quality control (in the admin's opinion), it is not reuploaded and if the admin is feeling nice, he tells the user it didn't meet the requirements for x reason.
If it does, it is uploaded via FTP to
thecoverproject.net/uploads/ready, as well as a thumbnail scaled proportionately to 360px wide.
Then the magic happens. The admin uses the page Snowcone sets up to "officially" upload it to the site.

Profit!