I think that we've discussed this issue before: Walmart refusing to print good photos. Judging from the quality of the photo that was rejected in the story I'm guess that most of the photos here would be rejected as well.

Question: What can possibly serve as proof of ownership of a digital photo?

the raw files would serve as reasonable proof, most cameras that would have a 'high quality' issue better be able to make raw pictures, and i think most photographers shooting something that is risking on the too good side would probably shoot raw in that situation, and i havent ever seen any ways of turning an 8-bit-compressed jpg into a 12-bit-raw file, and no discerning pro photographer would give out his raw files

I'm sorry I think this is halariuos. Who gives a darn if it is pro or amateur or not. they get paid do they not? They should follow a ethics code as all other developers. If its not your don't print it with out permision.

Exif data? Take the camera in with you and let them watch you pull the card out. It may be that you just uploaded images to the card with another device, but at least it is a little more convincing. I have found that Walmart is overpriced compared to other photofinishing stores. So, have a look elsewhere instead of being drawn there by the low price advertising:-)

ok i know on my camera (cant speak for all) it keeps a memory of all of the settings and title of photo that could serve as proof since i have mine set numerically such as
DSCN2572
DSCN2573
so if you were to have that photo log with the original titled photo it may work

however i prefer to have my prints done at somewhere better because my walmart does a horrible job... i actually prefer price club the most as you load the images on their computers and it sends to their printers without the clerk working inbetween but they could still reprint i guess... if you really want to be safe about it take it home load it in photoshop and sign some sort of a tag on the photo then go have it printed

Well, the answer to this problem is clear. If you want to print a photo there, just choose the really bad ones.

I'll have to start putting myself in every shot. Prepare for a lot of extended arm self portraits. Seriously, this could be a trend that other chains will pick up.

or you could sell a vital organ or two and buy a fuji pictography mini lab, do it your self and give Walmart the bird. (a bit pricey but a small organ should cover it....)

$3500 for the Pictography 3500 (any print upto A3) which is almost twice as cheap as it is here in the UK - worth a cornea any time of the day :-)