All you need is an image editing program. Pause 
the video at the desired frame, hit "print 
screen" to capture whatevers on screen. Bring up 
your image editing program, create a new blank 
project, then use edit-paste(ctrl-v). At this 
point you can edit/crop/etc. Then just save out a 
gif or a jpeg. Screen capture is an OS feature so 
this method doesn't require really any special 
sftware other than an image editor and there are 
enough free ones available. 

Free options are nice. Note if you want a high 
resolution capture this may not be the best 
option. This description is a Windows users, you 
can do similar things on Macs, etc, you have to 
look it up though.