On Wikipedia, the images you use must have a what's called a "free license".

Anyone who creates a work is automatically the owner of its copyright, unless they produced it for an employer, or transferred their copyright to someone else. A free license is a kind of copyright license that says the creator will allow anyone to use their work (with some, or no, restrictions) without asking for permission.

Wikimedia Commons — the free media collection that Wikipedia draws from — defaults to what's called a "Creative Commons Attribution Share-Alike" license (CC BY-SA).

That means that anyone can:

• use it, copy it, share it
• modify it and share it as a new work

As long as the person using it:

• provides credit to the original author and notes the license (Attribution)
• releases any modifications of the work under the same license (Share-Alike)