When I start DNGKonverter and click at the "+" button to add files, "all image files" (in german: "Alle Bilddateien") is preselected. Now I try to add JPEG files for example. This operation fails without an error message. It just does not do anything. Only if I add RAW files it works. 
If DNGKonverter is meant to work with RAW files only, then all the other image file formats should not be offered as input formats. And trying to add a format like JPEG, that is not supported, should produce an error message.

Reproducible: Always

Steps to Reproduce:
1. start DNGKonverter
2. try to add a JPEG file
3.
Actual Results:  
nothing

Expected Results:  
either an error message or the JPEG file should be added to the input list

See http://www.everydaylinuxuser.com/2014/04/the-kde-picture-editing-software.html what happens, when an unsuspecting user/reviewer, without much knowledge about image processing, checks out DNGKonverter for the first time.