Regarding thumbnails:
You may already know this, but an image has height and width properties so you can change it's rendered size on the page. Unfortunately, it takes the same amount of time to load as the larger version, so it may work better for you just to create a resized copy of your original image to have as your thumbnail. Anyway, here is some code...
HTML Code:
<img src="myimage.gif" height="200" width="300">