I have always made the assumption that if you post an image online, no matter what website, there will be ways that people can download it and then re-use it.
Some sites such as Facebook and Tumblr make it extremely easy for users to download posted images in whatever resolution they were uploaded albeit with some probably loss of quality due to the web site’s image “viewing optimisation” process.
Some websites like IG, Flickr, 500px, etc do an OK job at making it hard for users to download images, but if one really wanted to, they could use a screen capture tool, or with a tiny amount of programming knowledge gain access to the higher resolution image files through manipulation of URLs (yes apologies, I briefly did test this just to see if it can be done before I wrote this post) – although it seems most websites are now making this harder to achieve. If you are not a programmer, a search of the web can usually find third party tools to download Instagram, etc – although I am not sure why anyone would bother downloading the poorly compressed, low res IG imagery – but its not that hard to do. This does NOT mean that I condone abusing an online image site’s terms of use, I am just pointing out that it can be done and so you should assume someone will do it.
Many online image hosting websites like 500px.com also offer to automatically apply an ugly watermark to your images (or you can do this yourself in Adobe Lightroom, etc before uploading them).
Google research has just posted a blog on how AI software can easily and automatically remove most watermarks effectively – see HERE for the post.
It seems that if you want to make it harder for AI to do this, you not only need to introduce randomness to the position of the watermark but a random warping of the watermark.
I guess randomly warped watermarks will come in future versions of Lightroom – but for now it seems that all your efforts with watermarking may be in vain and just makes your photos ugly.
So current state, your watermark will be easily removed thus assume once uploaded, there is a risk others could abuse your image copyright without your permission.