The Snip macro is for making it easier to post screenshots here to the forum. It can be installed via the AddonManager.
Macro_Snip
Here is the screenshot I took in the above video.
The macro can take the screenshot itself (if it works on your system, so far I have only tested on Windows.) or it can use a screenshot you already took and copied to your system clipboard. If it finds an image on the clipboard it skips the first dialog, the one that takes the screenshot, and instead it uses the one it found on the clipboard. To bypass this press Shift key while invoking the macro.
The macro then takes this image and saves it to a temporary file, then opens that file in a file open dialog. You can drag and drop the file from the file open dialog. It will be deleted automatically when you close the open file dialog. If you open it in the dialog the macro will attempt to open the file in your default application for opening png files, for example it will open the file in Paint on my windows computer.
If the macro cannot work to copy the screenshots it can still be useful for screenshots you can take using other tools. Some other tools:
Windows -> Windows key + Shift + S
Linux -> gnome-screenshot utility
Mac -> Command + Shift + 4
Just use the other tool to copy the screenshot to the clipboard, and then run the Snip macro.