Use Sql Server as Your Indexing Engine
I didn't realize this until today, but not only does SQL provide the great full text search capabilities everyone knows and loves, it can also index binary content (.doc, .xls), etc. without much extra work on your part.
To get this cool feature working, all you need to do is add a column to your database that has the file extension of the content stored in your data field (must be image type field), and then when you set up your index, just tell SQL server that this column is the file type column and you are set. Now, you can run standard fulltext queries on that column and it works like magic. Very cool.