Printing a frame from a video

Is the system version shown bellow your question still valid? iMac 21.5″, macOS 10.13? Tif you just upgraded to macOS 11 Big Sur., the gears icon is no longer available. We are now having plenty of other editing tools for videos instead, but no longer the ability to extract directly a still frame. You can do it with copy and paste or with QuickTime Player as an external editor, see this user tip:

How to extract a Still Frame from a Video Clip in Photos 6 on Big Sur… - Apple Community

There are two options to save a still frame:

Save the current keyframe as the still frame (this may have a lesser resolution then the video itself):

Double click the video to open it enlarged. Click "Edit".

Use the video controls to find the frame you want and click "Make poster frame".

Click "Done".

Select the thumbnail of the video, use ⌘C to copy it and paste it into a Finder window. You will now have a new JPEG saved to the Finder.

Use Quicktime Player as an external editor. This way you can save a still frame in the same resolution as the video.

Select the thumbnail of the video in Photos and use the command "Image > Edit with > QuickTime Player.

When QuickTime Player opens, use the video controls to find the frame you want to save.

Use the command "Edit > Copy" or the keyboard shortcut ⌘C to copy the frame you want to save to the clipboard.

Now open Preview and use the command "File > New from Clipboard" to save the copied frame as a new image in Preview. This will open a new image with the name "Untitled"

In Preview use the command "File > Export" to save the "untitled" document as an image file in a high quality.

Import the new still image to Photos, if you want to save it there.