The answers depend on what has been said before.
If you already mentioned that your friend was going to send some pictures, you would introduce them as "the pictures". You would speak of them as "the pictures", the specific ones you mentioned before.
If you were talking about unrelated things and then, casually, just happened to take out some pictures to show, you would say these are "pictures". You would speak of them as "pictures" because they are not specific to your previous conversation.
I hope this helps