How to load image to collectionview from url obtained from json - iphone

Question

I have an IOS app that is using RestKit to pull json formatted data from a server into a CoreData Entity. One of the attributes in the data is a URL for the image associated with the particular article. I'm trying to load that image to my collectionViewController. This is what I've been trying with no success.
From within
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
I am trying this
NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSURL *photoURL = [object valueForKey:#"imageUrl"];
NSData *photoData = [NSData dataWithContentsOfURL:photoURL];
cell.cellimg = [[UIImage alloc] initWithData:photoData];
[cell.title setText:[object valueForKey:#"title"]];
If I comment out the attempt to grab and load the image the view loads great with a default image and the titles of the articles received from the json data. Based on that I know everything is coming in correctly.
I have also determined that *photoData is being assigned the correct URL. But each time I encounter the NSData line the console prints out "-[__NSCFString isFileURL]: unrecognized selector sent to instance...."
I honestly don't know if this is even the correct way to do this or if it will even work. I am pretty new at this so any help would be great. Given that I am new some small code examples would really help as well as explaining the proper way to approach this.
Just in case here is the header file where I define *cellimg and *title
#import <UIKit/UIKit.h>
#interface GlobismNewsCollectionViewCell : UICollectionViewCell
#property (strong, nonatomic) IBOutlet UIImage *cellimg;
#property (weak, nonatomic) IBOutlet UILabel *title;
#property (weak, nonatomic) NSURL *imageUrl;
#end

Answer 1

I think you are using NSString as NSURL. So try to use this one...
NSURL *photoURL = [NSURL URLWithString:(NSString *) [object valueForKey:#"imageUrl"]];

Answer 2

Thanks to Dharmbir I had this issue wrapped up within 25 minutes of asking the question!
To clarify for any new guys like me I changed the line Dharmbir suggested so the block looks like this now
NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSURL *photoURL = [NSURL URLWithString:(NSString *) [object valueForKey:#"imageUrl"]];
NSData *photoData = [NSData dataWithContentsOfURL:photoURL];
[cell.cellimg setImage:[[UIImage alloc] initWithData:photoData]];
[cell.title setText:[object valueForKey:#"title"]];
Notice the 4th line in the block also changed from this
cell.cellimg = [[UIImage alloc] initWithData:photoData];
to this
[cell.cellimg setImage:[[UIImage alloc] initWithData:photoData]];
I also had to change my *cellimg property to this
#property (strong, nonatomic) IBOutlet UIImageView *cellimg;
from this
#property (strong, nonatomic) IBOutlet UIImage *cellimg;
I had to change to the UIImageView class because the cell in my storyboard is based on the UIImageView Class. Hope this helps a guy in need thanks again Dharmbir!