Comment by dspillett

If there is a way of saving the result and posting it to the server (caveat: I have no idea if there currently is, there almost certainly isn't in a "95 of web users will have a compatible client" sort of way) then you could use this to remove some CPU load when accepting images that you want to watermark before presenting to other users. If it is your image being watermarked you are unlikely to circumvent the process.