My friend Craig was interested in making some t-shirts with a low res image. He asked me if i could enlarge it and make it "high resolution" so that he could send it to the company for printing. I told him that I didn't know how. He said he went to someone else and they did it for him. Yesterday he had the printed shirts at his door step and they look great. The image covers the shirt from top to bottom.
This is the only image he had to work with, at this exact size.
How did it get bigger without distorting, blurring, etc?