So you're planning to sell an image online and you want to post it in a way that gives your customer a good look at it but can't just be downloaded and printed out without you getting paid.
Here's an easy way to go from
I like the subtlety of this mark. If you do, too, here's how to do it in Photoshop.
Open your image. For this effect, I use the horizontal type mask tool (which you can access by clicking on the little triangular tab in the lower left-hand corner of the type tool in the toolbar (it's the one that's a black T).
Now, you need to choose a font. I like typefaces like Minion, Caslon, etc. - serif faces. You can pick the typeface and size prior to typing, and you will probably want to go large. On the photo above, I used 96-point type.
Click your type cursor where you want to start typing. I'm not sure you can conveniently move the type around when you use the mask tool, so choose carefully. If you can, choose a part of your image that is largely light *or* largely dark, but preferably not running from one to the other.
When you click your cursor, the image will get a startling magenta mask. Don't worry about it. Type your word, then to adios the mask, click on any other tool in the toolbox. This will leave you with type that is marqueed (with a blinking outline).
Now, you will need to adjust curves (either command-M or through the Image drop-down menu, under Adjustments. When you adjust curves, you get a pop-up box that features a 16-square grid with a diagonal line through it. Click on the midpoint of the line and drag up or down to make the type lighter or darker. You will see the line on the grid becomes quite curvy.
When you're satisfied with how the type looks, release the mouse and click OK in the pop-up box. You will still see the marquee lit up around the type. You can make this go away by just saving and closing the photo or by some other, more circuitous routes.