To put images into your sig you need to buy toriprime.
The maximum size of a sig pic is 400x100, unless it's animated in which case the maximum is 100x100.
You can buy toriprime for $10 for a year
here.
If you buy toriprime you get:
A longer sig,
Animated avatar,
You can put a picture in your signature,
You can change your usertitle,
And access toriprime only board.