So, I wrote a little online Exif viewer to view whatever data might be encoded. Here's a screenshot using the viewer on a picture from a recent post:

That's just the summary -- you can see the full data using the tool itself.

The amount of data encoded in the image is quite variable. Many times there's just about nothing, as the data is stripped somewhere along the way. Here's a version of the previous picture with most data missing. It's missing because it's a smaller version that's meant for web display, and for such use the data just makes the file bigger and slower to download.

Here's one with GPS location data encoded, which I think is quite cool. In the summary area is a link to a Google Map of the location, and below that is an embedded Google Maps pane. With either, you can switch between Satellite and Map, and zoom, etc. For some reason, though, the satellite imagery available to the embedded pane is of a much lower quality, at least for Kyoto Japan, so with this picture it's best to follow the map link in the summary.

You can also check images on your local hard drive -- images directly from a camera generally have the most information. Give it a try!

If you're using Firefox or Safari, you have the added benefit that you can install an Exif-viewer button on your button-bar toolbar. Once you've done that, later, when you're viewing a page with an image you want to check out, just click the button and you'll be whisked to a new tab showing the image's data. I find this really useful. It doesn't work in IE, though, sorry.

I use the viewer a lot on images I see in the Digital Photography Review Samples and Galleries forum. Lots of nice pictures in there. Many have their Exif data stripped, but many do not.

Finally, I should note that my viewer makes use of Phil Harvey's most excellent Image::ExifTool library. Thanks Phil!