Up to version 33, Kullo for Android stored images captured by the phone’s camera to be used as a sender avatar in the SD card directory “amfb”. The files are called img_xyz.jpg where xyz is a long number.
This was a mistake because Android apps should usually store their data in an app specific directory. We fixed the issue in version 34.
Since “amfb” is a public directory that might be used by other apps, the files cannot be deleted automatically. Feel free to delete those files using a file explorer or by mounting the SD card on your computer.
We apologize for any inconvenience.