There are actually several discussions on the cons of storing many image in a DB. I was curious what folks here are doing. I am not sure how you concluded that FB and other apps store images in DB. Are you sure they are not storing in a filesystem path inside the app? (Yes DB == database)
https://www.quora.com/Is-it-a-bad-design-to-store-images-as-blobs-in-a-database