You need to convert the screen print into an image file, eg jpg. This is possible by creating a blank image file, eg in Photoeditor, or any other image software, then pasting the screen print into the file. You may need to adjust the image size, then post it as a normal picture ...
If you are not sure how to capture a screen image, I use control+print screen ... this copies the screen into memory, which then can be pasted as above.
