1. Make sure that you keep your photos to a small size and keep the resolution to about 72dpi. What this means is that your photo will remain sharp for everyone to see but not sharp enough for people to enlarge and print.
2. The other thing that you can did is to add a watermark. Now having used Photoshop for most of its inception, I'm going to use it to demonstrate on. If you use a different product, you're on your own. Sorry!
Pull up your image. (I'm using one sent to me by its owner.) Select the text tool. Then using whatever font, size and color you want, place your text and hit enter.Highlight the text again (still in text tool, click in front of the first letter and highlight all of it). Now from the top menu, select:
LAYER: LAYER STYLE: BLENDING OPTIONS
Drag either of the opacity bars to the left. Your text will fade. For this example, I'm showing "general blending" at 32%. You want your watermark visible but not detracting from your photo.
That's basically all there is to it. I like to rotate watermarks right across the photo, making it even harder to remove. Because make no doubt about it: it can be removed. But it takes a lot of work. Work that your average thief isn't going to bother with.
Now a small reward for all of you still reading. These 3 photos are by Jan Granai, an ex-park ranger who because of lay-offs has taken up photography and making clay miniatures for her roomboxes. We've discovered that we have the same quirky sense of humor:
I think Jan will do well, don't you? Maybe I'll even get to see her roomboxes one day. (Jan, if you're lurking: thanks for the chuckle!)