   Printed image size?
  I have a 100x100 pixel image.How will its dimensions (in units of millimeters) be on a paper if I print it?Is there any other parameters that affect the printed size of an image other than its dimensions?   
  Printers take images in pixels, and a requested dots-per-inch (dpi).For a document at 92dpi it would be just over an inch.For a photo printout at 300dpi it would be 1/3rd of an inch.Photo applications can also do some behind the scenes magic, and scale things for you.You give it a target dpi, and a target output paper size. It then stretches the image it outputs to have enough pixels for that dpi and size.   