Hello civca,
unfortunately, this is not possible. The corresponding information is not available because referencing images via input components only references the image itself, but not the target resolution (exception is CMS_INPUT_IMAGEMAP). The resolution in which the image is to be output is only defined in the template source code. So the information in which resolution an image is used is not stored in the reference graph and therefore it is not possible to determine this information via API.
Depending on the URL creator used, however, you can identify in the generation directory which images are referenced in the original resolution. The standard URL creators append the resolution (usually separated by a "_") to the file name (e.g. mypic_myResolution.jpg), but nothing, if an image is used within the original resolution. However, this way you can only find the images that are generated on pages that are created and furthermore you cannot find the images that are directly included into the output file (i.e. PDF files).
best regards
Holger
