Bad Photo:

 Photo from Elie Yav.

This photo has bad composition because the depth of field is not focusing on anything and the subject is clearly posing for the photo and isn’t really capturing a genuine moment.

Good Photo:

 Photo from Marco Redaelli

This is a good photo because the depth of field is fully focused on the subjects (the birds) and not the background, the photo seems to be taken from very close for more detail, it is very simple because there is only the two birds and a blurred background, it is also symmetrical because the subjects are placed evenly and the birds are obviously not posing and are captured during a genuine moment.