I came across this gem on DZone this morning. It's a tutorial on storing images in a MySQL database (using PHP). There are several things in the tutorial that I don't agree with, but I'll let those slide. What really bugs me, is how it fails to mention that this is a very bad idea.
A relational database is not a filesystem. Files go on a filesystem. Relational data goes in an RDBMS. Repeat that a couple of times.
The most compelling argument for this, is performance. I did a quick test. I did a google image search on stupidity and downloaded the first 10 images. I then wrote PHP scripts to serve them up in two ways:
1. From a MySQL (MyISAM) table with 2 columns: ID (int, auto_increment) and DATA (mediumblob)
2. Using readfile.
The third test method, "FS", simply loads the image over HTTP directly, without any intermediary scripts.
The results are the average of running Apache Benchmark 10 times: 10 concurrent requests, 1000 requests per run.
As you can see, the MySQL approach is a hell of a lot slower than the more sensible FS approach.
The best way to store your images (or other binary files) is on the filesystem. Every modern web server does a good (or excellent) job of serving up static content. Storing them in a database is by far the worst possible solution. Not only because it's slow, but also because it complicates database backups: MySQL dumps with binary data don't compress very well, causing the whole database backup to be slower and larger than needs be.
So please, be sensible. Store your files on a filesystem.