[Freak_NL]

It depends.

Memes are not some special class of imagery; if the image used along with whatever text slapped onto it was specifically created as shareable art, then you are 'merely' in a legal gray zone unless the author provides an explicit licence statement (e.g., placing it in the public domain, or under some Creative Commons licence).

If it is the type of meme where a photo is reused, than chances are pretty high that that photo is (of) a copyrighted work, and the meme thus a derivative work. The same rules for any other type of photo apply: figure out if what you are doing is fair use, or needs attribution, or needs a licence agreement with the rights holder(s).

You may also need to look out for relevant laws beyond copyright; like the person in the photo suffering as a consequence of it being reposted (as nauseam) on the internet suing under whatever law is applicable. Johnny Memeposter on Facebook won't be sued, but your publisher might.

Also repeat the above for all relevant jurisdictions.