You have to provide the size of the image. Example: 250x320.

Also, what are you doing here? Were you looking for placehold.it by any chance? This is just a private version of that service I put up and modified for my own purposes.

Well, since you're here, the accepted parameters are size, type (gif | png | jpg), bg (hex value), color (hex value), fontsize, and text.

Don't be evil.