Blob Data

Can someone please show me an example on how to read & write blob data to a Database? For example if I have the query below (Northwind), how do I actually place the blob item in a picture box on a windows form?
SELECT Picture
FROM Categories
WHERE CategoryID = 5

Try the link below for two sample code to upload image in SQL Server. Hope this helps.
http://www.developerfusion.co.uk/show/3905/

http://www.dotnetbips.com/displayarticle.aspx?id=60

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All those tutorials simply store the file into a byte array and than write it to the databse.

I was always asking myself the following:

How big can a byte array become? Is the array's index an integer?

What do I have to do if I want to store a file which has more bytes than an integer?