[Major_Small]

While that's true, the major sites will resize your image on their site. When you're seeing a 'medium' image from something like Zooomr or Flickr, you're actually seeing an image that size that's already been downsized by that site's engine.

But for people hosting full sizes and using HTML to resize, it's still a benefit. I don't want to open a thread and see a 2500x3500px image on the screen. Having to scroll around to see it, and the havoc it wreaks on the borders and formatting of the board itself is very annoying.

Either way, a 500px picture is a 500px picture. Whether it's being resized by your browser, or has been resized by some other method (uploading to a popular image hosting site, or just resizing through editing software), unless your browser is woefully inadequate, it should have no problem figuring out how big 500 pixels is. Honestly, if your browser can't even measure pixels, it has no business being a browser. Showing images at the correct size would be the least of it's worries.