Logical Fallacies

 

These are all ad populum fallacies. The reason the dog is an ad populum is because it is clearly a dog, but the dog is generalizing that because it has four legs, as does a cat, it must be a cat. This dog could easily think it was a bear, zebra, or cow for that matter. Ad populum is an appeal to the people or the majority. This dog thinks that because all cats have four legs, like he does, he must be a cat because the majority says so.
The Pope is commiting an ad populum fallacy because he is saying that a billion catholics, or the majority of catholics, can not be wrong when in fact he is wrong. He is going with the majority of the people therefore the people can not be wrong.  
The third and final comic strip is an ad populum because the Muslim said that if one person thinks that all the one and a half billion Muslims are wrong than that one person is clearly wrong. The reply to this was the four and a half billion non-muslims couldn't pssibly be wrong. In actuality they all could be wrong and the majority has no true say in it if they are wrong.