So there is a picture I want to recover, and it has a preview that is full resolution, but it says unrecoverable. If it is overwritten and unrecoverable, why can I see the image in the preview?
The MFT entry for the deleted file holds the cluster addresses of the file's data. Recuva will go to these clusters and recover whatever data is in there. If the clusters have been overwritten with another file then that other file will be recovered. The overwriting file may itself be deleted but the data will remain unchanged.
So what you are seeing is possibly the overwriting file, which may be live or deleted. What does it say in the info pane?