The internet is a wonderful thing. You can find almost anything you want to online, with just a couple of quick queries and clicks of a mouse. This includes information, music and yes, your photos among other things. Now maybe you do photography as a hobby, or maybe you do it professionally. I'm guessing that no matter the reason you do it, you don't want your images stolen, used or reproduced without your permission.
Using watermarks on your images doesn't prevent your images from being stolen, and with all of the photo editing and manipulation software packages out there, it doesn't prevent them from being modified; however, it does provide you with the ability to brand your image, so that at least some of the not-so-savvy photo thieves out there will be giving your blog publicity when they pilfer your photos. Hey, it's better than nothing. In fact, while examining my server logs, I have found that some of the traffic I receive comes from websites that aren't even remotely related to my blog topic. When I check them out, more times than not I see that my image was used in a discussion board posting, blog posting, etc., but at least my watermark was still on the image displaying in all its glory, and thus leading to some traffic to my site.
If you're looking for a free, easy and effective package to watermark your photos, I suggest a piece of software named FastStone Photo Resizer. This software makes it a snap to watermark your photos, and also offers other great tools like photo resizing, cropping, and rotation, to name a few. The software is adware and spyware free, and is always being improved with new features and enhancements. It's a great alternative to Photoshop for the light photo editor (it's free for home use), and serves the watermarking purpose.