Your image html code update looks good. No problem there at all 👍
Beyond what was previously mentioned, you have two other items which are preventing your site from being mobile friendly.
The first is your Custom Insert. These are right after each of your first posts. Your table image needs the html for mobile which you applied earlier. Apply the CSS from my previous link, to that image in your Custom Island. Your Custom Island can be edited at:
Control Panel > Portal | Custom Islands
The second one is a bug in 760 that has been fixed in 761. its related to the Facebook images on the footer of each post.
The 760 bug was documented and fixed for 7.6.1 @ http://www.ubbcentral.com/forums/ubbthreads.php/topics/260038#Post260038
The fix for this Facebook iFrame is to just disable that integration in your Control Panel until you get 7.6.1+. This will remove the display problem. This does not affect Twitter at all. You can continue using the 760 Twitter integration without issue.
1) go to Control Panel > Display Settings
2) And then open the "Topic & Post Page Settings" section.
3) Remove the check-mark from the "Show Facebook "Like" Button" box.