Aside from the file format difficulties mentioned in the previous section,
there are a few other common causes of trouble with transferring JPEGs.

Old decoders that don't handle progressive JPEG will often give rather
cryptic error messages when fed a progressive JPEG.  If you get a complaint
like "Unsupported marker type 0xC2", then you definitely have a progressive
JPEG file and a non-progressive-capable decoder.  (See part 2 of this FAQ
for information about more up-to-date programs.)  Or you may get a generic
error message that claims the file is corrupted or isn't JPEG at all.

Adobe Photoshop and some other prepress-oriented applications will produce
four-channel CMYK JPEG files when asked to save a JPEG from CMYK image mode.
Hardly anything that's not prepress-savvy will cope with CMYK JPEGs (or any
other CMYK format for that matter).  When making JPEGs for Web use, be sure
to save from RGB or grayscale mode.

Photoshop also has a habit of stuffing a rather large thumbnail/preview
image into an application-private segment of JPEG files.  Some other
applications (notably early releases of Sun's Java library) are known to
choke on this data.  This is definitely a bug in those other applications,
but the best available workaround is still to tell Photoshop not to save
a thumbnail.  If you're putting up an image on the Web, having a thumbnail
embedded in it is just a waste of download time anyway.

When transferring images between machines running different operating
systems, be very careful to get a straight "binary" transfer --- any
sort of text format conversion will corrupt a JPEG file.  Actually that's
true for all image formats not just JPEG.