All of the jpg's I have created in InDesign CS 5.5 are identified as "unknown" file types when saved by InteractBuilder in the folder for the project, and are therefor unavailable as files within the app. I purchased a jpg online, and that file is identified properly. I've accessed the jpg's in other programs with no difficulty, and my operationg system (Yosemite) identifies the files as jpg's. I did save one of the jpg files as a png (which you can't do with INDD, unfortunately) and that is read properly.
Customer support service by UserEcho