You may want to read this about scanning and then printing a specific size.
http://www.scantips.com/
I still think the fastest way to accomplish what you want is to edit with
Paint, save the file and then open it with
www.faststone.org
then click on File and Print.
A window will open, for size, select "Specified size" and enter it. If the
original photo was say 15 x 10 centimeters, enter this. Then enter your
printer preferences and select the highest resolution. Click Print. As long
as the paper size in your printer is the same or larger than the Specified
size, you will get the print at the size you want.