Probably not.  It's just using an image file to cover up a .RAR file.  I imagine it could even fool CompuPic Pro (though I did once see a .ZIP that seemed to appear as a .GIF somehow).
I'm not really sure how someone could get into your file; they'd have to first suspect that something's wrong with the .JPG.  I suppose if you stored some big files, then the .JPG would appear really large and that could be suspicious.  If you're going to store a small text file (maybe a few passwords?  Not that I would recommend that) it could work all right, I think.