Do you store the image data in your database, or the image file name?
The code above looks like you are storing teh file name, but teh description reads as if it is the actual image data.
If it is the file name, that's easy: convert your byte to a string:
byte img = (byte)dt.Rows["logo"];
string s = System.Text.Encoding.ASCII.GetString(img);
Image1.ImageUrl = "~/" + s;
If it is the content, then it is slightly more complex.
Forgot to change "img" to "s" in final line - OriginalGriff[/edit]