What's this?
I know, there are some borders effects plug-ins already available.
But I didn't find any of them able to do this kind of frame:

...till now!
Download it!
Plugin Frame.dll
Here is the DLL
The source is available with the plugins package!
http://forums.getpaint.net/index.php?showtopic=7186
How to install
Close Paint.net
Unzip and (re)place the DLL in your Effect folder usually: C:/Program Files/Paint.NET/Effects
The User interface
This plugin is added to the menu Effects, submenu Render.

Choose the frame mode:
...Single border using primary color.
...Single border using secondary color.
...Double border using both colors.
...Frame with two reversed corners.
...Frame with four reversed corners.
...Frame with middle face with two reversed corners. New!
...Frame with middle face with four reversed corners.
Distance from the edge (0,200, default=0):
It's the margin.
Width of external border (0,200,default=10)
Width of internal border (0,200,default=10):
Width of middle border (0,200,default=10)
it's the size of each single border.
Transparency level: New!
Choose the transparency amount. It works better if you create the frame on a new emply layer.
Options:
...Check for same width amount: If checked all borders widths use the ‘Width of external border’
...Invert Primary / Secondary colors: check to invert colors.
...Add lines: A small line is added between each border.
The third color in mode for the middle face is the average color of primary and secondary colors and
The color for the added lines is the negative of the third color.
Some examples:
Model of image used:























