I never found any info on DPI either. What I found (probably what you found also) was the max total resolution they support is 17,000,000.. so max would be 5000 x 3333 for a 2/3 aspect or 4750 x 3562 for a 3/4 for example. That is what I sent for the 30x20 print. For a mug or t-shirt or one of the other items obviously a lower res would be fine. They scale the image to the proper size if it is large. I took the 20x30 prints to have them framed and I think they are going to look spectacular.