In the 1990s, “drop shadows”—simulated shadows
which make it appear an image is “floating” above
the page—were a popular feature in Web page design, but making
such images often required expensive, proprietary software. Our
pnmshadow
utility for the Netpbm image processing toolkit provided an open
source alternative, but wasn't available to users of
non-Unix-like systems. The
Shadow Server
allows any user with a Web browser to upload images in PNG,
JPEG, GIF, or a variety of other formats and receive an image
with a custom drop shadow added.