How to generate image with a string?

[sntshkmr60 at gmail.com]

More or less I'm trying to replicate placeholder.com in Python. I'll be using Django in the backend. Given all the parameters, I'm not sure how will I be generating the images.

 * I will be passing width and height of the image and maybe the text and background color. 
 * I also want to center the text vertically and horizontally.
 * The text size will be increased proportionally to the image being generated.

Can someone enlighten my path? What libraries can be capable of doing this?