Homebrew How does Pokémon Su /moon and other games know what photos taken from other scources are not from it

[Hepointatsquib]

Sorry if this doesn't belong here or my wording is a mess, but I'm wondering how certian 3DS Games know which photos were taken within that game (For example, in Ultra sun/moon you couldn't put an image in the SD card with other photos from that game, as it wouldn't reconise it)


I'm mainly wanting to know because I find it a little intresting, plus i want to use Ultra sun to put "stickers" on a funny image

 

[Subtle Demise]

I'm not entirely sure myself, but there are plenty of ways it could be done. Could be a special header, or maybe even the image is digitally signed.

 

[Bene-Hrethgir]

The image is signed digitally, I have never actually seen any discussion about this before(prolly as the applications of such are slim to nill) if you have CFW(Luma, ReiNAND ect.) you can just take a screenshot of the picture then do w/e it is you plan on doing (Luma outputs png screenshots)

EDIT: Namesnipe is right it takes .bmp not .png screenshots

 

[Namesnipe]

The image is signed digitally, I have never actually seen any discussion about this before(prolly as the applications of such are slim to nill) if you have CFW(Luma, ReiNAND ect.) you can just take a screenshot of the picture then do w/e it is you plan on doing (Luma outputs png screenshots)

I believe it's bmp, not png.