Watermarking or tagging images that appear online is a common security measure meant to prevent the circulation of a particular image without attribution. The ease with which images may be copied, dragged, screengrabbed, or otherwise extracted from their original context and distributed through platforms such as Tumblr means that those interested in selling images or otherwise controlling their distribution often rely on digital watermarking as a blunt proprietary tool.
Digital watermarking can be accomplished in a variety of ways, but is most commonly a name or phrase placed over the image itself, thereby disrupting its visual continuity and making it undesirable to copy. The most recognizable watermarks are those of stock photo agencies such as Getty Images, and many artists, such as Guthrie Lonergan, Kevin Bewersdorf, and Aleksandra Domanovic, have used Getty photos as a means of reflecting on issues of copyright as they apply to affect and art making.
That said, the practice is hardly limited to artists and large corporations, and has become particularly prevalent on eBay for users selling "authentic" or "vintage" photos and prints. The simultaneous need to display the image for the buyer but prevent the buyer from simply copying the file itself makes watermarking a widely agreed upon convention. How this marking is accomplished varies widely, and in some ways produces a kind of self-reflexive visual poetry, one primarily concerned with questions of authenticity and attribution.