Most GoPro and action cameras have a timelapse feature that will take photos at set intervals (usually various from every few seconds to minutes) That would probably be the best bet for getting photos of better resolution then a screen grab from a video. You'll have to make sure the camera saves the photos though instead of automatically compiling them into a video.
The downside is that it will do this for the entire duration of your ride and you'll have to find the one photo you want.