I working on a site that displays images from a variety of other sites by having elements that link directly to the other sites. Some of the images are high resolution and some of there are not. In the case that many high res images are being displayed the website performance goes down. Is there anyway to display the externally linked images at a consistent (reasonable) resolution so that less bandwidth is consumed and site performance does not falter?
No, not really. If these are images out of your control and you're simply linking to them, there is not much you can do.
One option is to create some kind of pre-loader with a progress bar. You'd have to download all the images, process them into smaller images then display them. however, you're not really saving any time doing this since you'll still be downloading the images in the first place.
You just need a class name on the element that the images are going into. You probably have a bunch of div's with different sized images in them. You need <div class="mySize">...</div> and then, mySize {width:100px; height:100px;}.