It can be done, but what are you using for a DBMS?
For example, at my workplace we are using SQL Server w/T-SQL on my current project, and we use the Image Data Type to help achieve what you are looking for (MSDN Article)
Doing the above can be costly, especially if you have a lot of high-res images. So with that in mind, you could alternatively have a table with a key field and value field that points to the image path on your application server.
e.g.
KEY | VALUE
BannerX | ~/Images/Sponsored/BannerX.png
BannerY | ~/Images/Sponsored/BannerY.png
BannerZ | ~/Images/Sponsored/BannerY.png
If you make the Key field the primary key, then you will only need to add future C# code if you add new keys to the Database.