This is what I posted in forum as
https://social.msdn.microsoft.com/Forums/en-US/bf48b450-6ee4-408b-a441-a53b23c75346/failing-to-insert-a-large-image-into-powerpoint-slides-using-setselecteddataasync-in-officejs?forum=appsforoffice

It seems this is a limitation or bug. We are using setSelectedDataAsync with base64 encoding to copy the image into slide. but the image is corrupted if the image size is relatively huge (like over 5MB). The same code works with both Word and Excel. I guess something went wrong with PowerPoint.