Highest possible image resolution for "Oswald creative wordpress portfolio" theme

Seems that some theme however they claim providing a professional platform to act as a “portfolio” still they are unable to deliver it.
This is about the main personal image that one can upload into “Oswald creative wordpress portfolio” theme.
Share with me your experience if you think differently. I am not impressed at all so far with its performance.

Uploading a low resolution image can potentially be very dissuading. Wish you all a nice rest of the week!