Pixorize is a free tool for adding interactive annotations to your images. Using Pixorize is a fairly straight-forward process. To get started just upload any picture that you have saved on your computer. (After your image is uploaded you may need to resize it to make it fit into your browser). Once the image is uploaded you can add points, circles, squares, and stars as annotation markers on your image. After adding an annotation marker you can write text to explain the element of the image to which you are calling attention.
To save and or share your work on Pixorize you must create an account. However, creating an account didn't require validating your email address (I created an account with a fake email address that I have for one of my dogs). After saving your image on Pixorize you can share a link to it or embed it in a blog post as I have done below.
Applications for Education
Pixorize is still a new product, but it has great potential as an alternative to Thinglink. You could have students use Pixorize to annotate diagrams, maps, or images like the one in my example featured above.