gistfile1.m

NSURL *appURL = [NSURL URLWithString:@"instagram://app"];

if([[UIApplication sharedApplication] canOpenURL:appURL])
{
    // Image
    UIImage *image = [UIImage imageWithContentsOfFile:imagePath];
    
    // Post
    [UIImageJPEGRepresentation(image, 1.0) writeToFile:[self photoFilePath] atomically:YES];
    NSURL *fileURL = [NSURL fileURLWithPath:[self photoFilePath]];
    
    self.dic = [UIDocumentInteractionController interactionControllerWithURL:fileURL];
    self.dic.UTI = @"com.instagram.exclusivegram";
    self.dic.delegate = self;
    if (message)
        self.dic.annotation = [NSDictionary dictionaryWithObject:message forKey:@"InstagramCaption"];
    
    [self.dic presentOpenInMenuFromRect:CGRectZero inView:nativeWindow.rootViewController.view animated:YES];
}