Resolution: 1024 x 640. Fill at least 70 % of this area. (Bigger resolutions can influence results heavily)

Image Format: JPEG

Image Compression: Recommended 100 or at least 90%.

Do not forget to set selfie as:

Java

setSelfieImage(selfie);

Preferred orientation:

Incorrect orientation can heavily affect results (Issue is observed in release of IEOS 7.7.3.).