It's distressing seeing an animal injured, it's also infuriating seeing so many pets put at risk by their shit owners and it's just weird that people are posting telling you you're legally/financially/morally responsible.
It's okay to feel bad for the dog, but in which country would you be responsible for the vet costs, when it's the owners responsibility to keep the dog safe?
Edit: I would only approach the owner if you feel you can do so safety, you don't know how people will react, explain what happened and leave.
Hopefully that's a useful suggestion for your memes.