You'll need a flickr ID or a Yahoo ID to upload photos, but that's it. When you're viewing any listing, just click the "Add your photos" link, login to flickr, and upload an image. We'll take care of tagging it so that it appears alongside the correct listing.
Want to do it manually, or add tags to existing photos so they appear along with the open mike listing? Just add "openmike" (no quotes) and the keyword for that listing as tags. For example, the Art Land Bar listing is located at:
The part after "listings/" -- "artlandbar" in this case -- is the additional tag you'll need. Just check the address while viewing any open mike night, you'll see the keyword in the same place each time. After any flickr review period (as often happens with new accounts there), your pictures will automatically be accessible from that listing. Note that only the most-recent 5 pictures will be shown as thumbnails with the listing; all the rest are a click away.
Update: canned this feature. Just didn't work out well, and a simpler solution is now in place.