Delicate subject. The dogs do use the beach as their dumping ground, literally. There is human trash, but nothing comparable to the picture supplied and it is not representative of our beach. Some trash comes in from the ocean from whatever source it originated. Many beachgoers pick up their trash, put it in plastic trash bags and leave it for the garbage truck. Unfortunately, loose dogs and wild animals tear apart the trash bags and the wind blows it everywhere. I have had to pick up 20X more trash on the road behind my house than on the beach. I built a wooden frame so the animals can not knock over the cans but still have trouble. I have also seen do-gooders walking the beach pick up trash in the wet sand and throw it up much higher on the dry sand so as not to go back into the ocean.
Unfortunately, we are not going to make all dog owners more responsible. We are not going to solve the trash bags being torn open or the occasional litterbug.
Sadly, I have never been attacked by litter. I have been attacked by dogs off-leash many times. But that is not allowed to be discussed nor shamed.