I don't think it'd be indelible... for a tattoo to be permanent, it has to go into the lower layers of the skin. The top layers, that would soak up things like chemicals, eventually come off in the form of dead skin that your body constantly renews. Short of obtaining a third degree burn and then cyanotyping over that (which I DO NOT recommend, third degree burns are serious business but it's making the point about how deep the pigment has to go into the skin...), it wouldn't work.
If you're really interested in having a tattoo done, I'm sure you can get prussian blue pigments (though there's probably better ink/pigment choices) and most tattoo artists can do a direct photocopy of whatever you want and then transfer it to your skin and tattoo through that with a proper tattoo needle and ink. The biggest problem with transferring photographs to the body is... the body moves. It grows, it sags, it's three-dimensional not flat like a piece of paper, the skin and cells constantly renew itself and you get very slight jostling of the ink. It will eventually get a little bit blurry over the years. I've learned that with just the past 10 years of having my tattoo.
Also would be wary about the suntan/sunburning idea but only because I was very unfortunate as a child, in my little stroller, falling asleep with my hand on my knee and for years and years and years, and as i grew up, i developed a "monster print" on my knee. It *might* not be noticeable now that I'm 28 but it was when I was a teenager and I don't tan much in the first place. Again, skin sags, moves, etc. you may end up with an ugly square with a blob in the middle.
Mark Fisher - you'll probably find that a "magic eraser" which is a very very very microscopically fine abrasive, will get rid of all your blue staining except for anything that has sunk into porous materials. Prussian blue is a solid material suspended in water/liquid but very fine... so it can appear to stain but it's not very hard to get out of non-porous materials like plastic trays etc.
