Short answer: 1024×768 will produce consistent and great images across ALL of the technology : Perfectly Clear corrections, Face Detection, Beautify and Red-eye.
Long Answer: It’s possible to use a smaller image size, but the risk is inconsistent results. For example, if you used a really small photo in 1 application, and a larger one in another application.
- Perfectly Clear Core Corrections: 1024×768 is a good minimum size target, but the corrections will be applied to images as small as 50 x 50 pixels.
- Red-eye: 1024X768 is recommended as minimum, lower resolution is discouraged as the detection and false positive rate of the correction might be affected
- Face Beautification: there are no limitation as to the resolution of this image, although there are no guarantees in terms of quality for images smaller than QVGA (320×240)
- Face Detection – it can detect faces as small as 50 x 50 pixels