Can your digital camera be used as a photo viewer?

I thought I tried this once in my Lumix, and it could not recognized
the JPEG files. I wonder if others ever try and whether it works only
for certain cameras. I did not try it desperately, and perhaps I did
not place the JPEG files in the right folder of my camera card. Or
perhaps I need to rename the photos so that they should follow the
name conventional system of the camera (such as DSC for Sony, P for
Panasonic, etc). Thanks for the discussion.

PS. What I mean by using the camera as a photo viewer is either:
1. A set of copy of downloaded JPG photos from the same camera, but
they have been retouched or modified (although they still called by
the same file names) OR
2. Completely obtain JPG files from anywhere and dump them in the
camera card and insert it into the camera, and hit the "view" button.

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I thought I tried this once in my Lumix, and it could not recognized
the JPEG files. I wonder if others ever try and whether it works only
for certain cameras. I did not try it desperately, and perhaps I did
not place the JPEG files in the right folder of my camera card. Or
perhaps I need to rename the photos so that they should follow the
name conventional system of the camera (such as DSC for Sony, P for
Panasonic, etc). Thanks for the discussion.

PS. What I mean by using the camera as a photo viewer is either:
1. A set of copy of downloaded JPG photos from the same camera, but
they have been retouched or modified (although they still called by
the same file names) OR
2. Completely obtain JPG files from anywhere and dump them in the
camera card and insert it into the camera, and hit the "view" button.

The answer is "not easilly". Each camera make and model is different so I
will have to give generalizations that may or may not fully apply to your
equipment.

Some cameras keep a hidden file on the card that keeps track of the last
number used and such. If there is an image beyond that number it will not be
found by the camera and thus not viewable. Next the cameras assume that they
are looking at photos taken BY that camera and so will only accept images
that match exactly the output of the camera. So if the folder or file name
is wrong, rejected. If the image size (in pixel dimensions) is wrong,
rejected. A slight difference in format imposed by an editor (maybe as
simple as an expanded or reduced EXIF) could cause rejection. There are
probably other reasons that a camera would reject an image for viewing, but
these are the two most prevalent.

There is a program out there (I don't remember the name or address of the
free download at the moment, but it will be posted by someone in a few min)
that is specificly made to adjust images to match the file and location
expectations of many popular camera brands. Even this is not 100% perfect
(tho it tries).

Your best bet is to either get one of the new photo wallet devices, or an
Ipod, to do your post shoot/edit/download display functions. I have even
seen an infomercial about a tiny photo wallet that is about the size of a
thick credit card that will display most photo types. Sure the display on
these is tiny, but most camera displays are not exactly 8x10's either.

Randy