You actually have the tension too tight. The tooth marks in parts of that filament are at about 40% depth. What happens when the tension is that high, is that the filament starts to mash into an oval shape, which will cause it to jam when it tries to go into the top of the hot end. (Ovals don't fit in the hole, it has to be round.) When it jams, the filament will strip and chew up a lot of little crap and get a spot in it where there are no tooth marks.
But looking into your gear, I can see all kinds of stuff in the teeth - it looks like shreds from previous attempts to force the filament down have caused the teeth on the extruder gear to get all clogged up. That means that you have less tooth to catch in the filament, until you get to a certain point, and then the unclogged teeth are catching too deeply.
1. You need to remove the filament drive and clean the debris out of the teeth on the extruder gear. Until you get all those little shreds out, you won't be able to catch the filament and feed it in.
2. You need to loosen the tension quite a bit. All the way, actually. PLA requires almost no tension. (After you clean out the extruder gear.)
That should get it going again.
Since i had a minute this morning - i wanted to show you what I think I see in your photo. (Hard to tell with black filament.)
