I can't send Photos on my iPhone 4?

Every time I attempt to send a picture on my iPhone 4, it will load like 3/4 of the way and say that the message can't be delivered. Is this a setting on my phone that I can change, or could it be an issue with my cellphone carrier?

Well you can always check settings go to messaging and make sure mms is turned on. If it is and still won't work then you should contact your carrier because mms may not be in your plan.