Joecar2000 - To do that very easily, you can use the free Avidemux - even if you never use it for anything else.
Install it, open and close it at least once before using it.
To extract stills - open Avidemux, and find your camera clip. If you can open the directory with it in on the Desktop, you can drag'n'drop the video file(s) into the Avidemux window - easier than Pathing each if you want stills from several clips of an event.
I think your 5D2 clips are H264/MOV at 1920 x 1080. When you drop the clip in, Avidemux will ask, "Do you want to change modes?" For this purpose, say No, and continue.
The video will open in a large image window. Make that more manageable by going to the bar, View > Zoom 1:2.
Use the Slider to find the section of the video you need to extract from.
Use the 2 centre Arrow-buttons in the line of 6 shown bottom-left of the dialog, to go forward-back frame-by-frame.
When you have the clearest frame possible, go to "File > Save > Save BMP Image". Click, and the window that opens lets you browse to your Destination directory.
While it also has the JPEG option there, I use BMP, as that's a far less "lossy" format than JPEG to work on, if you want to Crop, use Levels, Sharpen, etc.
You can (with JPEGs) also Extract multiple frames - use the A-marker button, click it at the start of the sequence. Then blue-arrow forward, say 10 frames, and click the B-marker button.
Then do "File > Save > Save Selection as JPEG Images". If you leave the markers where they are, look at the say, 10, JPEGs, and realise you like No.7, but it needs some "fixing-up" - you can go back and re-select that frame as a BMP, better to modify.
Dave.