Good Image Editor for Youtube Video Sprite Ripping

[ZetTheLegendaryHero]

I don't know if this is where I should be asking this question, but there are some youtube videos that aren't from games that I would like to "rip sprites" from for either mugen or a fan game and I was wondering if anyone knew of a good free image editor to do that with. I have a way to download the videos and convert them to images I just don't know if the image editor I am using (paint.net) is the best for this.