>I would like to transform a jpg. picture to a variable, store into into a memo file and encrypt it by
>changing some character of the file. As I don't know anything about low level issues, I would
>like to know if changing any character of the file is really a safe way to protect it.

A blob field type is better for storing binary data. You can use http://www.sweetpotatosoftware.com/SPSBlog/PermaLink,guid,5d4a0cf0-7d1d-4353-a49b-667946ff1c81.aspx for encryption