If the game itself have to have some screenshot command in the first place then for 99% those games will not be supported:
- BlazBlue: Continuum Shift II
- Dead or Alive Dimensions
- Mario and Sonic at the London 2012 Olimpic Games (however I will re-check this one)
- Tales of the Abyss
- Tekken 3D Prime Edition

It's a bit sad we can't upload other image-based stuff, however it has one little explanation (a bit overdone tough)
Maybe Nintendo did it this way so we won't accidentally upload photos that would put us in embarassing/difficult/&c. situations or allow others to do so
After all Nintendo 3DS is console for everyone...

I guess it should stop us from posting Questionable stuff.
It is a Webbrowser Site so we can upload Screenshots mid game (which is great) but it would take only 30 seconds longer to plug out the SD card and post the picture manually.

For Europe It was told on the Website that only Animal Crossing works atm. I dunno how the program even recognizes the screenshots tbh. I sure need to do some experiments with it.

I would take a wild guess that Animal Crossing like his Wii version has some special built in stuff that allows to make screenshots from the game and then those screenshots are saved with the use of some special(?) codec so no "plain usual PNGs" can be uploaded

However yeah, with SuperCard DSTwo I can do screenshots from both GBA and NDS games without much wuss, I believe there will be possibility to do the same with 3DS games when (if?) proper flashcard will be made (no spoiling~) then whole idea of this site will be kind of killed because who would be crazy enough to not use plain old imageshack where he/she can post screenshots from any game VS special-special site with only one game possible...
Gee sometimes Nintendo scares me, I have a lot of respect to them but sometimes they seriously go insane...

I guess it's Resolution based. The 3DS Cameras capture JPG's of higher resolution than the 3DS Screen. However the build in AC: NL Screenshot Function captures Screenshots with the same resolution as the 3DS Screen. I think I'll make a Pic on the PC with the proper resolution and check if I can upload it from my 3DS. Then the "List of supporting software" would change into "List of Games with Screenshot Feature"

Ok I fucked around with that app
Screenshots from KH3D didnt work
Self made screenshots dont work
Camera pictures didnt worked
Only animal crossing Photos
...
A friend of mine thinks that screenshots are flagged snd that ninty decides what you can post. Kinda like a Region Lock for Screenshots...

Probably works in a way similar to the camera application, you can't view anything that wasn't created with that app either.

you can view everything with the 3D Camera...
it just has to be JPG and have a supported resolution.
The transfer App even showed alle Pictures I had on my SD card but I was able to upload only AC:NL stuff...
Its feeshy since since in the last N-Direkt Mini they told that every game with a screenshot function could use this App to upload screenshot yet still I could do it only with AC:NL...
Here http://puu.sh/3K0lS.jpg It does work... but if its only with AC:NL then it is really Lame

Really? Nothing ever showed up on mine (although I did only try it just when I got it, which is already over 2 years ago, so maybe something changed in the newer firmwares).

I even put a bigger version of my old Avatar on the 3DS that was way bigger then the screen and it worked. back then Too.
This Screenshot is also viewable with the 3DS Cam http://puu.sh/3KOw1.jpg (Faking things is fun!).
And downloading pictures from the 3DS browser also works for bigger pictures however the maximal Resolution is met quite fast.
Anyway updated first post since got few Information from the US site of this function. This website works with every region and has same QR code.
Also no words about other games working just ACNL...

This post has been edited by Tibia821, Wed, July 24th, 2013 at 20:22