Some images suddenly have placeholders on website

HI,

I am noticing lately that some of my .jpgs that were added some time ago to my media library are still there and they’re still visible in the editor, but when I go to view it on the website, it only shows the caption or alt text, just a placeholder. These images were appearing just fine before on the website.

Would you be able to please let me know what is causing it?

Here are 2 links that have this problem:
https://specialneedsinmycity.com/page/2/
https://specialneedsinmycity.com/tipsandtricks/from-teachers/
Theme: Twenty-ten
WP version: 4.2.1

the picture that is working has a url of
https://specialneedsinmycity.com/wp-content/uploads/2013/05/gini-weiss1.jpg

the picture that doesn’t has a url of
https://specialneedsinmycity.com/wp-content/uploads/2013/04/Richards.jpg

Thank you in advance.
specialneedsinmycity.com