On MacOS 10.13.2 using "Standard" Application Mode to scan files that are all only JPGs, it works and finds exact duplicates.

Using "Picture" Application Mode generates the following error traceback:

Application Identifier: com.hardcoded-software.dupeguru
Application Version: 4.0.3
Mac OS X Version: Version 10.13.2 (Build 17C88)

Traceback (most recent call last):
File "build/dupeGuru.app/Contents/Resources/py/cocoa/inter.py", line 259, in pulse
File "build/dupeGuru.app/Contents/Resources/py/hscommon/gui/progress_window.py", line 101, in pulse
File "build/dupeGuru.app/Contents/Resources/py/core/app.py", line 323, in _job_error
File "build/dupeGuru.app/Contents/Resources/py/hscommon/jobprogress/performer.py", line 43, in _async_run
File "build/dupeGuru.app/Contents/Resources/py/core/app.py", line 780, in do
File "build/dupeGuru.app/Contents/Resources/py/core/scanner.py", line 137, in get_dupe_groups
File "build/dupeGuru.app/Contents/Resources/py/core/pe/scanner.py", line 31, in _getmatches
File "build/dupeGuru.app/Contents/Resources/py/core/pe/matchblock.py", line 167, in getmatches
File "build/dupeGuru.app/Contents/Resources/py/core/pe/matchblock.py", line 65, in prepare_pictures
File "build/dupeGuru.app/Contents/Resources/py/core/pe/cache_shelve.py", line 129, in purge_outdated
File "build/dupeGuru.app/Contents/Resources/py/core/pe/cache_shelve.py", line 47, in delitem
File "build/dupeGuru.app/Contents/Resources/py/shelve.py", line 128, in delitem
KeyError: b'id:14964'