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

[Alen]

You can also try decreasing the dpi value of the image

DPI has nothing to do with file size. If the file is 72dpi or 3000dpi still the same amount of pixels. DPI is for printing.

You can decrease the file size by blurring out the parts of the image that are not important, this helps but you can only push it so far.

I think the best solution is to user agent sniff and send the correctly sized image. Instead of sniffing out mobile, sniff out desktop users and only send them higher file size image.