After looking back at it, I missed the fact that the single image sits inside a repeater field. I do know repeaters are a pro feature.
Still, can I downgrade?
Regardless of the fact if I downgrade or not.
Installing the free version, disables the pro version. So I lose the image.
But deleting the free version and enable the pro version again. The image is not coming back. Aka the blog I am working on for a client now has hundreds of missing images. I am glad I made a backup before trying it.