not2easy - 7:04 pm on Jan 6, 2013 (gmt 0)

If you do not need the transparency (alpha-channel) of .pngs you should stick to .jpg and putting high resolution images online is a waste of bandwidth because many screens cannot render images at high dpi resolution. Filesize affects pageload speed and while most visitors are not on dial-up these days, no one waits for huge images to load. Some people have a plan limit that charges them more for using extra bandwidth so they would not appreciate those big files.