Image Background for Border WPF

Question

Hello, I'm new in C# technology, specially in WPF - that's why I wondering for one thing.

 

 I want to realize some nice but simply functionality. I have to do application like small bar in upper part of monitor so I have a few corporate backgrounds (diffrent collors end etc), all of them have the same size.

 

I created as WPF application, I make no Windows style properties, make transparent and etc. I added Border do Form. I also add all pictures do resources of application and I changed build for them to "Resource".

 

And now the most "complicated" part. How I can assign image from resource to background of border? Specially that I want to use some iteriation or something, for choose random picture from resources (application should run once with this background, once with another) etc.

 

I know that I ask much, but is there possibility to do this?