Why am I getting this error?

[UnknownBallin]

This is the second plugin I've had this exact error with. I have no clue what's wrong on my end?
Error: "Call to undefined function tim03we\slashskin\imagecreatefrompng()" (EXCEPTION) in "plugins/SlashSkin.phar/src/tim03we/slashskin/Main" at line 45

[tim03we]

It's probably the PHP binary.