Recently, I and my colleagues, we are discussing how to build a huge storage systems which could store billions a pictures which could searched and download quickly.
If you are really talking about billions of images, I would store them in the file system because retrieval will be faster than serializing and de-seralizing the images
When dealing with binary objects, follow a document centric approach for architecture, and not store documents like pdf's and images in the database, you will eventually have to refactor it out when you start seeing all kinds of performance issues with your database. Just store the file on the file system and have the path inside a table of your databse. There is also a physical limitation on the size of the data type that you will use to serialize and save it in the database. Just store it on the file system and access it.
The answers above appear to assume the database is an RDBMS. If your database is a document-oriented database with support for binary documents of the size you expect, then it may be perfectly wise to store them in the database.
It's not a good idea. The point of a database is that you can quickly resolve complex queries to retrieve textual data. While binary data can be stored in a database, it can slow transactions. This is especially true when the database is on a separate server from the running application. In the database, store meta-data and the location/filename of the images. Images themselves should be on static server(s).