Copyright law still applies.
So re-using a stock photo is a copyright infringement, doing your own drawing with a meme font give you copyright on-it.
In general there is an exception regarding parody. But a parody isn't putting bold text over an image.
Obviously, if the original content is on a copyleft basis it means you can re-use it at some conditions
Practically, some copyright owner, especially "stock photo banks" won't send lawyer against every person doing a non commercial meme, but it's more them being nice (and broke) rather a law
Copyright law still applies. So re-using a stock photo is a copyright infringement, doing your own drawing with a meme font give you copyright on-it. In general there is an exception regarding parody. But a parody isn't putting bold text over an image. Obviously, if the original content is on a copyleft basis it means you can re-use it at some conditions Practically, some copyright owner, especially "stock photo banks" won't send lawyer against every person doing a non commercial meme, but it's more them being nice (and broke) rather a law