I think in the internet, art theft simply is a topic.
However, I think uploading low-resolution files (or rather: with small size, not with small quality) would be an idea. I personally do that for a while now, cropping my picture to about the size I want to upload it, and maybe only make it one step smaller by DeviantArt. Using the DA watermark would be an idea, though I'm not sure how well that works - I guess one can photoshop it out quite easily.
Another option would be to upload things in "small size", and to cover it with watermark-lines (I saw this here, for example: A Fox Named Fable). The artist in the sample made this very well I think, as the writing doesn't "disturb" the picture itself.
Also, there are pages where you can register your artwork, like saying "this is mine". I can't find the names of them right now; however, some of them also charged money for their service, or only had so-and-so many artworks registered for free.
The easiest way to avoid art theft is digital watermarking. This doesn't just make it harder to steal from your account, but if yiur work gets shared on tumblr, instagram, and elsewhere it can bounce all over the place, quickly losing its attribution through no act of malice. I know I am forever trying to track down amazing pieces of art and being unable to (even with Google Imager Search) and I like to share the amazing stuff I find, and even when trying to be scrupulous about crediting the artist (not least because, if you like this, "here's some more") and water marks make it easier to do that, even if I forget the attribution and link.
My problem is somehow someone was able to remove the watermarks on my artwork and obtained the high quality images themselves. I don't even know how you could do that? When I was uploading I was using the deviantart watermark and choosing lower resolution posting. I also started signing my working gimp, I'm not sure if that is digital watermarking or a form of but I obviously did something wrong...
I've got a few different methods I've used so far but it didn't seem to matter. One was the standard DA watermark, two was on separate layers in gimp but when you export as a jpeg it shouldn't matter, and the third one was to make a copy of the original and ruin the copy with a direct watermark on the image. It didn't look photoshopped out, and it looks more like someone had access somehow to the originals but I don't give out passwords, and I only share my computer with my hubby so I'm mega confused. The other site was sloppy copycover or whatever someone told me my stuff was on there- the obvious DA watermarks were on the images. I don't think I really care it looks like a scam site.
Social media just seems like a big joke most of the time causing more stress in most cases than needed. Certain platforms are worse than others so I stay away from them. I don't use fb often and only get on to talk with my family.