One of the tricks mentioned in here -- changing the extension to bypass a check -- works great on a ton of sites. Many sites won't let you upload a .gif file, b

One of the tricks mentioned in here -- changing the extension to bypass a check -- works great on a ton of sites. Many sites won't let you upload a .gif file, but don't actually check the contents of the file, so just rename your .gif to a .jpg and voilà! (you can sometimes get this to allow you to upload and execute server-side scripting pages too)