I published an article on the Cooking.stackexchange blog yesterday. I shot all photographs in a standard 3:2 side ratio, but when I inserted them whole, I didn't like the appearance. I asked for help in the Graphic design chat room, and Pankeej gave me a great idea: to cut out interesting parts of the images in a size which looks good when inserted into the post (650x200px) and link them to the standard versions (650x430px). I did this, and the blog post looks good now, but I was afraid that nobody will notice that the images link to bigger versions. I asked a friend whom I had sent the link, and he admitted that he didn't notice at all that there may be links to bigger images, despite the fact that his cursor gets changed onhover.
To make the matter even more problematic, there are other pictures in the post which don't link to anything, because they are already embedded in their largest size. Also, there is one picture which is visually different from the others, because it has a caption, and Wordpress adds a whole box around the picture for the caption.
How can I get readers to notice that they can click on some of the pictures for a larger version? I like the way the pictures appear now in the post, and I don't want to change their appearance drastically, e.g. by adding a thick border or something similar. Also, this is hosted on a WordPress instance administered by Stackexchange, and I can't install more plugins or similar. I must be able to solve the problem with simple HTML, or image editing.
This is how the article looks like:
This is what the reader sees after clicking on the wide blackberry image.