Just the way you're giving string type for your username member, you will be giving a specific data type to your Image member.
It depends on your framework of application, to choose which object type for your data.
Bitmap
[
^],
Image
[
^],
byte[]
[
^] and all other such data types can fulfill your need of defining an Image object. You can then -- when required -- convert them into graphics object to represent your data.
In SQL, image field is also a field that contains arrays of byte. Which is given the value of byte arrays of the image (actually a file) and then can be retrieved as byte arrays and converted to files and so on.
I would also tip you, to not create another member while using getters and setters. Use it like,
public string Username { get; set; }
This would have the same functionality of retrieving the Username and setting the Username and so on.