Hi Paul,
I can't speak for the PBase folks, but I believe that the EXIF data is extracted from information embedded in the image file (usually a .jpg). The EXIF data is created by the digital camera.
From my observations, PBase gathers the EXIF data when the image is uploaded the first time, and aside from values with are already editable (camera, date, tech notes, etc.) you cannot edit other EXIF data (metering mode, white balance, etc).
Note: Some photo editing software will not preserve the EXIF data in an image when changes are made and you save. Photoshop
does save EXIF data, I don't know about other programs...
I have heard of programs which allow you to create and edit exif data for a jpg (I think one was called EXIFer) but I haven't used any myself. It might be easier just to use the tech notes field
Hope this is helpful,
-Mike