Here are the answers from a spectrum of science-artists.
- - -
"Most of what I sell online is original watercolor paintings and collages. I think that makes it a little less risky for me, as far as having my images ripped off, because it's very hard for someone to recreate the look and the texture of an original using an image from the web. But I know that someone could take one of my designs and put it on a t-shirt or a notebook.
On the other hand, I've been featured on lots of blogs and gotten show opportunities because people have seen my work online. The bottom line for me is that having lots of pictures of my work on the web has been worth the risk. So far, anyway!"
I place a value on the work I create, therefore I believe it's worthwhile to do what I can to protect it from infringement. There are a few websites I use to promote my business, so it's necessary for me to put samples of my work online. I make them relatively small and/or I place a watermark on them. I'm well aware that it's not a perfect system, but in my mind doing nothing to protect my images might indicate that I do not value them and it would be a disservice to the clients who commissioned them. Some might perceive that trying to protect one's work online is futile, but I wholeheartedly believe that just because an endeavor is perceived as futile doesn't mean it isn't worth the attempt.
By all means use my photographs! They don't do anyone any good just sitting on my hard drives. But be respectful of the fact they take time and money to create. At least have the decency to inform people where they came from. And if you are using the photographs to make money, I deserve some of it. After all, these photographs would not exist, and could not exist, if I was unable to earn a basic living.
Every time an artist puts their work online, it's a trade-off. Sure, it could be ripped off. However, in science-art, the audience-niche can be very small. I often paint fossilized winged trilobites on stone, and at the moment the audience who enjoys these paintings is not huge.
A niche audience has benefits. By blogging, tweeting and being a part of the science social media world, I gain community, friends, fans and clients. The benefit of community is that its members will also help to protect you and your artistic work.
Allowing artwork to be shared under Creative Commons is essential to community-building. It helps an artist gain recognition among people who enjoy the artwork, growing the community of people who respect your contributions.
I put my name and url on my artwork; I put my name in the image filenames. From my experience, the artists in the greatest danger are those who's online presence is obscure. Engage, and the community grows along with your career, as well as being half the fun.
Definitely post your artwork on the web, as publicity is always a good thing. The only true theft to be worried about is a publisher sniping it in my opinion, but this is easy to prevent by simply uploading a lower resolution version of the piece requiring a real publication to approach you for a higher quality version. As for people cross-posting your work, I won't worry as much about a lack of credit (though that is annoying), but rather the purposes and use of the work is often more of a problem in my opinion (in my case creationists). To make sure unwanted entities aren't using your work it is definitely a good idea to use Tineye.
The benefits of sharing and promoting my work online far outweigh the potential losses of someone stealing an image off my web page for profit. Additionally, I don't know of a way to protect your art online without seriously damaging the presentation. Watermarks, for example, prevent any real appreciation of the work. So my best advice is to upload images that look great in your online portfolio, but are not hi-res, with your url small and tastefully in the corner. In the very rare case that Big Company Inc. steals your image for their Big Marketing Campaign then I'm sure you can find a lawyer happy to help you both out.
If by "protecting artwork online" you mean preventing someone from gaining access to your web based images - you can't.
The only way watermarking can prevent image use is if it's so onerous as to render your image unusable for anything, including promoting your art. Keeping images too small to reproduce elsewhere likewise makes them too small to be useful for showcasing your work. Invisible embedded watermarks, which add a layer of "noise", can degrade image quality as well.
If your work is in print, anyone with access to a $50 scanner with a de-screening option can make a much higher resolution copy of your images than you are ever likely to put online.
The single best way to protect your images is to register them with the Copyright Office (they don't have to be published, you can register an "unpublished collection" of multiple images).
For image files posted online, a simple copyright line and the addition of your domain name, placed on the image in a way that doesn't detract from the effective presentation of your art, increase the chances for image credit to find its way back to you if the image gets reused, and provide the ability to say legally that the initial version of the image was identified as yours.
It may also be worth adding your domain name to the filename of the image (people are lazy, and will likely just use your original image file, unless you force them into a screen capture), e.g. "dinosaurcartoons_com_600.gif" (extra dots "." are not allowed in a web filename).
If you need to be absolutely certain your images are safe, put them in a drawer and don't let anyone see them.
My thanks to everyone above who gave us their thoughts!
How do you protect your artwork online? Answer in the comments below!