For some text elements or blog posts you may want to include a thumbnail image that links to a larger version of the image, as illustrated here:

This requires you to make two versions of the image file. 

1. One image file should be created with the dimensions for the thumbnail and the other image should maintain your normal dimensions. 
2. Upload both images files to the desired location on the server.
3. Insert your thumbnail image and create a hyperlink to the larger version of the file.