Reply To: How can I flatten all images in InDesign?

Yes, you can embed images into a InDesign dokument, but no matter what you do, you can always extract it back again. If you can see it – you can extract it.

So Yos, you CAN flatten/merge raster imagtes into InDesign files and pdf,. but you can always extract them afterwards.
You can protect a file from editing by adding a password – but if you can see it, you can always make at “printScreen”, and get the images that way.

Best (only) way to protect you art, is by writing that you own the copywright, and that sharing og re-using the art is not allowed.