Re: How big (file wise) should my background image be?

[Paulie_D]

Mass confusion entered in when image pixels were mapped to screen dots in web browsers. A 200 pixel image shows up as 200 pixels in a browser. How large it is, measured with a ruler, depends on the dots per inch of the screen. The image metadata might say it’s 200 ppi or 72 ppi or 1 ppi, it will still occupy exactly 200 screen dots. The world remains fixated on “72 ppi for the web,” so the question of “what’s the right resolution for web images” keeps coming up, and the correct answer, “it doesn’t matter,” keeps being supplied ad nauseam.

The real issue, if I understand it correctly is Pixels Per Inch (PPI).

There’s a handy discussion with a lot of useful information here:
http://graphicdesign.stackexchange.com/questions/6080/what-is-the-difference-between-dpi-dots-per-inch-and-ppi-pixels-per-inch