To my dismay, one of my works has been stolen.

[faberryman]

your settings on flickr allow the image to be downloaded at a relatively large file size, so it would be fairly easy for someone to use it.
consider changing the file size you upload to the web to discourage unauthorized use.

Not only is the image size large, but the resolution is 350dpi, which means someone can make a nice large print. Consider uploading images at a resolution of 72dpi and a maximum size of 720p on the long side. It won't affect how they look on the screen, but it will make them less attractive to download.