The VG Resource

So, I've got a small question about sprite ripping with a specific type of game. Considering the topic of rom hacks, mods, and fangames, do you need permission from the original creators of those types of games to do sprite rips of them, or can you just do it freely as you want? I've noticed how in addition to dedicating an entire section to edited and custom sprites, you guys also have multiple sprite rips from some rom hacks, mods, and fangames, so that's why I'm asking this question out of curiosity here.