This highly depends on what do you mean by process. If you want to do something complicated, I would recommend OpenCV since it offers a vast range of functionalities you can use to process your images.
That being said, if by process you mean extract text from images, you could take a look at Tesseract which is an open source OCR. If you will be going for an OCR, you could use OpenCV to do some pre-processing to make the text extraction process easier and more succesful.
If I am understanding you correctly, then you could take a look at this tutorial which should do what you are after (you start with an image and end up with a pixellated version of it).