Many of us now have digital cameras and just have choice pictures printed. So we either hand over our SD card or save digiscrapped pictures in a memory card to the printers. The thing is, those printing centers' computers are usually filled with viruses that may threaten our own computer memory. No matter how much they scan at their end or how much we scan in ours, we risk contamination.
One wise thing I practice is to save pictures I want printed in the smallest available memory card I have and then immediately reformat that card after. This way, I don't store many files in an 8 gb thumb drive and risk getting all of those contaminated.