I came across this recently, and though it may be old hat to anyone who is a seasoned astro imager, thought it could be quite useful for anyone starting out
Interesting link above but I found a quicker way to Save pics for the web. Rather than their method for saving in Jpeg the long way, I resize in Photoshop, then I just click on 'Save for Web'.
It is then converted to Jpeg and thumbnailed in one click.