Container fields don't hold only images, and not all images have a dpi, some are just a total pixal count with no size/dpi saved with the image, such a GIFs.
So some files may not return the same types of values.
Do you have different types of info being returned by files of the exact same file.extension?
Right. I'm just wondering what are all the possible items that could be returned by the function.
Currently the only values one can get are "remote:", "size:", "DPI:" and 4-character prefixes corresponding to files in managed storage (compressed/uncompressed files, images, audio, video, and PDF).
Relying on the list of all possible values is not a good idea, because the list may change when support for a new image/audio/video format is added in the future. GetAsText() output for all external containers starts with "remote:", so if "remote:" is not there, then the container is not external. HTH.
Thanks for the great info!