Question to Experienced Bloggers

I have a question, and if any of you know the answer, please leave a comment and let me know!! As you can see, I post a lot of pictures. Oftentimes, the pictures I post CANNOT be expanded by clicking on them. But sometimes you can click on them and they will expand, very rarely. I add the pictures the same way every time. But this is really getting on my nerves because many of the pictures I post are collages, which makes some of the individual pictures small and hard to see without expanding. I would like my readers to be able to expand these pictures by clicking on them. Does anyone have any advice on how to make certain my pictures can be expanded from now on?! Thank you so much!!