Fluid Images – a little script that automatically resize your images.
The script is needed to get fluid images resizing smoothly in Internet Explorer earlier than version 8. Otherwise, you can just use a simple CSS fix.
The script cycles through your document, swaps out the images for a transparent GIF, and applies the AlphaImageLoader property to each one. Then, whenever the window’s resized, the script automatically recalculates the proper, proportional height and width of the image, and resizes the spacer graphic accordingly.