It's hard to see from the pictures but it is either a bent blade/spindle shaft or an unlevel deck.
If you are able to safely get under the deck with a mower lift or similar you can check to make sure that the blades meet on the same level plane in the middle of the deck. Then while the mower is on the ground you can check the side to side level of the deck. If you had a bent blade or spindle you would typically have some type of noise or vibration.