Conditions for getting a image

What are the conditions for getting a image with the following API?: e.g., supported file extensions.
/Documents/{id} response sometimes did not include /Image URL.

REST API:  /DocuWare/Platform/FileCabinets/{fileCabinetId}/Documents/{id}/Image

Dear Kohsuke Namihira! It looks like the Community cannot answer your question. That's why we have opened a Support Request with the Number SR-143440-H5V5D for you. A Software Support Specialist will contact you directly to follow up. We will update this thread with the solution as soon as we have resolved the Support Request. With best regards, DocuWare Support Team

The /image call should work for each file type that can be shown in Web Client viewer. The only exception for this are data sets, meaning documents with only index data and no actual file attached to it.