Hi, I think the simplest way to answer this questions for your customers is to say that if they provide an image in jpg format the quality of the image will be very poor and it will not be possible to provide full (3) colour screen printed images.

This is because jpg images are specifically designed to work at the lower resolutions required for viewing in a web browser but screen print process requires high resolution images in a different format such as TIFF/EPS. EPS provides the higher resolution i.e. it contains more information about the image and ability to create three colour seperations needed for screen printing.