Just went thru this. I, as it happens, already own some of the Gear Whose Name Shall Not Be Mentioned and used that. Based on my limited experience, you will, in general, need some sort of image editor to adjust the results to match the print (and possibly adjust pixel dimensions depending on the organizer's requirements). I use Photoshop Elements which is pretty inexpensive; there are others, some perhaps free that might be sufficient. (But your query may get redirected to our sister hybrid photo site.)

DaveT