I’m confused about your issue with copying and pasting images with swiftkey. I do it all the time with no issues. Long press copy image - > long press paste. I just tested it copying it into text messages and emails to make sure I’m not insane and it works flawlessly.
Where does it say that? The abstract explicitly says that neither gboard or swiftkey collect or share the input content or frequency of specific characters entered.
Does it say differently in the actual paper?