If you need to store file in documents directory, use like this,
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0]; // Get documents folder
NSString *dataPath = [documentsDirectory stringByAppendingPathComponent:@"Images"];
if (![[NSFileManager defaultManager] fileExistsAtPath:dataPath])
{
[[NSFileManager defaultManager] createDirectoryAtPath:dataPath withIntermediateDirectories:NO attributes:nil error:nil];
}
NSString *imageFilePath = [NSString stringWithFormat:@"%@/%@",dataPath,@"upload.png"];
UIImage *image = [UIImage imageNamed:@"image"]; //Here place your image
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(image)];
[imageData writeToFile:imageFilePath atomically:YES];
If you need to attach image in facebook, use this statement,
[slComposeViewController
addAttachmentData:UIImagePNGRepresentation(image, 1) mimeType:@"image/png" fileName:@"upload.png"];