This is a nice, straightforward application that correctly encoded and decoded a short (2736 bytes) Objective C source file I had lying around into a rather large (2.7 MB) .jpg.
However, the .jpg side is a bit problematic. It apparently dropped the Profile that was embedded in the original jpg, changed the dpi from 180 to 72, dropped a number of other JFIF bits and bobs that I don't care about very much, and increased the file size (to 2.9 MB), while also introducing a small colour shift visible to the eye. Except for the colour shift, the output jpg appeared visually identical to the input jpg.
It would be nice if it could re-attach the original Profile to the new .jpg, and maintain the dpi and any other "important" tags. I don't know whether this would cure the colour shift.
I'd guess the file size is harder to maintain; I don't know much about the jpeg spec and common practice, and am not sure whether the original compression specs are recoverable from the input jpg. If they can be recovered, it would be nice if they were re-applied. I imagine the file size increase is at least partly due to the difference in compression specs.
Given an understanding of the limitations, this appears to be a pretty useful application.