Well, if it's for something like underage porn, don't bother. It's only a matter of time before you get caught. The sooner the better.
Recently reading the history of "Tank Man" though, made me take a closer look at this subject. Tank man is of course the Chinese protester who stopped the entire column of tanks with a simple, nonviolent stand down.
The "tank man" picture was literally one of the most prolific pictures of the 20th century... and it took some guts to SMUGGLE IT OUT OF THE COUNTRY. This goes to show there are many legal and ethical reasons for wanting some pictures concealed from the wrong people...
I like the idea of having a backup decoy card. That would really take the suspicion off of you for sure. With micro SDs though, there are a million places to stash them. One idea that comes to mind is bubblegum. If getting searched by a cop, they'll ask you to spit it out... it will be hiding in plain sight. If it gets x rayed, well most chewing gum these days is actually made from PLASTIC, believe it or not, so it may just blend right in. You could even stick it on the bottom of your shoe! NO COP is going to dig through your nasty used bubble gum for evidence... EVER.
Another idea would be to put it in a slit in your shoe. Behind, or in your wrist watch. Also, something like a ring, necklace, earrings or other piece of modified jewelry may be a good idea. A hearing aid may work well too.
Really, think about anything that a person may carry on them. Cigarettes. A cigarette lighter, matches, change, keys, gum, mints, candy, chapstick etc. They have rubber sleeves you can put over your keys (with little happy faces or whatever) people use to color code them that would work great to slip a micro SD under in a pinch.
Swallowing one would probably be a no go. I've read of them being recovered that way. So it would probably be best to save yourself the agony of the "extraction process" to just hand it over if it came to that. The only way out of that one (maybe) would be to encrypt your files with "trucrypt". From what I understand, they can't make you hand over your passwords in the U.S. but can most everywhere else.
The next safety precaution would be to "layer" your photos with something like Lolcatz or pictures of boobs or whatever. You can remove the top layer with photoshop and viola, good as new. That way, if they intercept your SD, they will just see grumpy cat and not the shocking news coverage you just obtained.
I found the best security is done in layers. Not just one method, but several. It's also best if done "hiding in plain sight". People don't search for things that are literally staring them in the face. It also increases the chance of "plausible deniability" if you get caught.
WHO PUT THAT THERE!