When transferring onto hard substrates, I suggest images be at least 200 DPI (at print size) to look good. Only 150 DPI is needed (at print size) when transferring onto soft substrates. Web graphics, which are often 72 DPI, give you poor and typically unacceptable results. “At print size” means that if you’re transferring an 8-by-10-inch image onto a hard substrate, the image needs to be at least 200 DPI. Especially useful for large tile murals, On1 Perfect Resize is a software tool that I use to quickly enlarge images without loss of sharpness or detail.
-David Gross, Condé