Out of curiosity, tell me what happens when you try to save these jpegs. These are not attachments. Instead, they are jpegs which somebody posted directly to the site by use of the {img} tag.
1. load this thread, and try the top image. It's a jpeg. It's stored offsite but is being parsed here via the {img} tag.
2. same idea, different user and different host site for the image file
Also, have you tried doing it with JPEGs outside of Akiba-Online? Specifically, have you tried doing it on other forums that use vBulletin version 3.8.1 or vBadvanced CMPS version 3.1.0, the versions listed for Akiba-Online?