Why do so many images I save from the -boorus have transparency? Many of them it doesn't even make sense. I see images I want to upload on /e/ but they're like 8 megs so I open them in paint and covert them to .jpg to reduce the file size and oh hey, once again for the 5 millionth time the reason they're so big is they have a pointless transparency layer.

They don't need them since the entire image is filled, is it some setting in a common image software? Is there a way we can teach people to stop adding pointless transparency layers before uploading them somewhere? Or is there some reason to have them I'm just not aware of?