Topic awaiting preservation: Printer vs Print

Why is it that an image doesn't need to be as good in quality when you
print it on a printer to look good as an image you send for print?

I mean, I have an image in 300 dpi. If I make it 200% and print it out
it still looks good but I guess you can't do that for print, right?

have you tried?

300 DPI is a "rule of thumb" - there's no magic here. In fact, 300 DPI is only meaningful for an average sort of magazine; it's way too high for newspaper to use an example.

So the success of printing at less than 300 DPI depends on several factors, including:
- the viewer's opinion of "quality"
- the image (some do better than others at lower res)
- the paper and printing standards (believe me, the same image reproduced in your local newspaper, in People Maazine, in National Goegraphic and in the CocaCola annual report will look mighty different!)

So - try it! 200% you might find you can get away with.