There are many observations and we try to draw conclusions from them but it is very difficult to make a proof for something very wide and big because the flow of time between the universe and us is very different (relative). it can easily happen that we are sometimes not right. The photo with the black hole was a year-long observation until the scientists were sure that it was a black hole and that the phenomenon described by Einstein is seen there.
There are many observations and we try to draw conclusions from them but it is very difficult to make a proof for something very wide and big because the flow of time between the universe and us is very different (relative). it can easily happen that we are sometimes not right. The photo with the black hole was a year-long observation until the scientists were sure that it was a black hole and that the phenomenon described by Einstein is seen there.