The only way to protect images (completely) on the web is to not put them there in the first place. Bad solution. If you are a professional you cannot sell very well this way. If you are an amateur you cannot share this way. If you are a camera club you cannot attract new members this way.
The partial solution is to only put up relatively low resolution images. I am bold and post images with a maximum dimension (either height or width) of 600 pixels. You can still (if you are good with Adobe PhotoShop) create a half-way decent 8x10 photo from that. I would not be satisfied with the resulting 8x10, nor would anyone who really appreciates a sharp image. Bottom line here: if you are paranoid about your images getting stolen, do not put up anything larger than 300 pixels in the longest dimension. If you want to share (or sell), post images in the vicinity of 600 pixels in the largest dimension.
Some people put a copyright symbol and statement in their images. I personally believe that in most cases this is a waste of time to stop theft. It detracts markedly from the image. It does stop people who are honest, but they are unlikely to steal the image in the first place. It does stop people who are computer-illiterate. But anyone adept with Adobe PhotoShop can take a really complex image with a huge copyright notice on it, and eradicate the copyright mark in just a few minutes. The result will not be perfect, but it will certainly look as good as the original image, and better than the original image with a copyright mark on it. The one time you might want to add a copyright to an image is if you would actually sue someone who used it. Lawyers and all. Few of us would bother.
Here is the secret that means you cannot protect an image except by not posting it: all the computer-savvy person needs to do is use a screen-save (aka Print Screen), and paste it into a blank (new) Adobe PhotoShop image that is the same pixel-dimension as the computer screen. Then you crop out the image you want, process it, and print it. This cannot be stopped except by not posting the image on the internet at all! Nor can someone photographing the computer screen be stopped, although the results here are a bit less satisfactory than just doing a print screen command.
For my personal website, if someone wants the images (and if 600 pixels in the maximum dimension is sufficient for them) then they are able to steal my images. Sharing is more important to me than preventing the thefts that likely occur. I have had several people ask to use my photos, and I always say yes, but not for profit. By the way, the images I compete at camera club are 1400x1050 pixels for digital, and 2200 by 3300 pixels for slides. The images I use for prints are 4200x3300 pixels.