How can my app send MMS with a photo?

Question

I would like to compose a message from my app which I can include a photo, for example: I entered my album in the IPhone and open a photo I can click on option and then on MMS tab and the photo will be added in a message and I can send it then to a whatever contact I want. what I want is that when I click on a button on my app, a message window will open with a photo from my resources in the XCode, how can I do that?

Answer 1

Manu's answer is good for iOS6, but for iOS7 they've finally made the user-flow easy:

MFMessageComposeViewController* composer = [[MFMessageComposeViewController alloc] init];
composer.messageComposeDelegate = self;
[composer setSubject:@"My Subject"];

// These checks basically make sure it's an MMS capable device with iOS7
if([MFMessageComposeViewController respondsToSelector:@selector(canSendAttachments)] && [MFMessageComposeViewController canSendAttachments])
{
    NSData* attachment = UIImageJPEGRepresentation(myImage, 1.0);

    NSString* uti = (NSString*)kUTTypeMessage;
    [composer addAttachmentData:attachment typeIdentifier:uti filename:@"filename.jpg"];
}

[self presentViewController:composer animated:YES completion:nil];