The ArcGIS Survey123 field apps for iOS and Windows do not limit the acceptable image format in image-type questions.

Workaround

Use a constraint to check whether an attached file is a .jpg (or any other format). Using ArcGIS Survey123 Connect, add a hidden question and reference the image question in the calculation column. Add a regex() constraint with the string to check. When the mobile worker attaches a file and attempts to submit it, the constraint error is displayed in a pop-up window if the file type does not match.

Steps to Reproduce