Adrian,
I have an application that takes pictures of items and uses them as evidence in a report.
These images are saved and then used to generate a report.
Each item averages 10 photos and I have about 2 million photos currently, with an average growth of 1 million photos over the next year.
I think about using it within the database because of the ease of selecting records with the content of the images (when necessary).
I think my biggest concern is to continue to use this strategy for the next 2 years and encounter a PostgreSQL limitation or some failure and have to migrate database again or have significant loss of images. And on the contrary too, if I use it on disk and in 2 years I find some failure or file limit in the operating system (currently it's windows server 2016)...
Related to this is the backup service that seems to me that in a disaster, I can restore the database relatively quickly if it's in the database. On the disk, I believe that the restoration is much slower and I don't think it's reliable that all the images are copied/restored.