If you are using the image from the 1st scene at that contrast. You did not brighten the scene enough. You need to desaturated color and flatten the contrast as well as brighten the image. That will make them appear very pale. The dark shadows with disappearing and you will be able to see his scrotum clearly. There is a split second when you can see the smallest part of his shaft entering her. It is not the moment from the image that you posted. It is when he has his hand on her butt cheek. Once you brighten it properly, You should be able to tell the the movements and angles are consistent with actual penetration.
But, some of you won't believe it unless you see an entire shaft from head to base go in. And then you will say it is AI.
Also, I realize that this is not a determining factor but I will mention it. At the very end of the seen. you can see that the condom has been used. Condoms don't look like that without penetration. I can guarantee you. No director or special effects editor would go through the trouble of staging a used condom for this low budget production.