ANY protection method can be slapped aside, as HTML is "insecure by design" -- any method -- be it javascript, javascript or... well... since javascript is the only client side language you would have access to, javascript, can be slapped aside in seconds. From document inspectors like firebug and dragonfly, to document information like the web developer toolbar's "information > document size", to simply using a cache browser, trying to stop it is effectively impossible.
Which is why usually you'll see things like watermarks -- one of the BEST watermark methods is to put the images behind a user login (assuming you have some sort of subscription service) then encode the visitors IP and account name into the image file in realtime. Takes a bit of server power to do, but it means when someone grabs the image and uses it somewhere else, you at least have a CHANCE at figuring out who took it and ban their account...
... but that's mostly only useful AFTER they've leeched you dry, to protect new content, not the existing stuff.
Bottom line, HTML just doesn't work that way; if you don't want people leeching your images, don't put them online. That's harsh, but it's also the reality of it.
