If you decide to use your own illustrations on your blog, I would suggest you do the following.
First, if you able to, edit the Alt text to include both a description of the illustration and your name. This serves three purposes. It means that anyone who is sight-impaired and using a text reader will have the description of the photo read out to them. It also means that if someone’s screen is not displaying graphics, they will see a description of what is supposed to be there rather than just a blank space or an error message. It also means that your name is embedded into the description of the illustration. This makes it slightly harder for anyone to rip off your illustration and get away with it.
The illustration above is taken from my newsletter provider. The illustration below is taken from this blog. Note that “Alt text” is not designated as such. However, it is possible to insert a filename into the illustration, which I think amounts to the same thing. If you’re in the same position, I suggest you do the same.
Second, set up a Google Alert for your name. This should ensure that if somebody uses your illustration on their website you will be notified.
Third, as part of the caption (you should always include a caption to accompany illustrations), include your name and copyright.
Fourth, if you don’t wish to include the copyright information in every illustration, do what I’ve done and place a footer on your articles stating your name and “All rights reserved” or a Creative Commons licence if you so wish.
In fact, you might want to do that anyway.