Remember kids, especially if you draw a lot and want to make a living with art, or even just a bit of pocket change:
If a stranger approaches you and promises you fame and USD 100.- in exchange for exclusive copyrights, you just say NO.
Reason 1: Exclusive copyrights mean that you don't get to use your own work anymore without the ok of the one owning the copyrights now. In all the contracts I signed so far, the company allows me to still use my works for blogs, portfolio, poster shops, merchandise and other things. And I can sell the original drawing too, if I want to.
Reason 2: USD 100.- for exclusive copyrights is a rather offending joke. Exclusive copyrights for small scribbles easily get over USD 1000.-. A caricature can go for USD 800.-. And those are rarely known for the high quality art, but rather for the sarcasm in them.
What most people want is the confirmation that their image won't be sold to other publishers. And that can be done easily