IPhone 4 not letting me send pictures?

I have had my iPhone for almost a year and up until a few weeks ago, it was fine. But recently I noticed that whenever I send a picture through iMessage, it says delivered, but the other person does not receive it. But this does not happen when I send them to people who do not have iPhones. I'm just wondering if maybe there's a certain setting I should check or if this is something I should contact verizon about.

I get this with my friend all the time, i don't have an iphone and get a "blank picture" of a camera with a? Most of the time. If you repeatedly send it it will usually go through.

I think that iphone somehow changed its pic data and not all phones can read it.