Received memory warning in UICollectionView iOS 7-Collection of common programming errors

I am using UICollectionView to show all the images available in my library using assets, its displaying all the images but when I scroll up and down many times , I receive a memory issue in the device and after some time it gets crashed saying CRASHED DUE TO MEMORY PRESSURE code used are as follows

creates here the collectionview and settings its delegate

UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];
allPhotosCollectionView=[[UICollectionView alloc]initWithFrame:CGRectMake(5, 5, 310, 481)collectionViewLayout:layout];
[allPhotosCollectionView setDelegate:self];
[allPhotosCollectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];
[allPhotosCollectionView setDataSource:self];
[self.view addSubview:allPhotosCollectionView];

delegate methods

- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section
{
return [allImageArray count];
}
- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView
{
return 1;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:       (UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath   *)indexPath
{
return CGSizeMake(95, 100);
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
NSString *identifier = @"Cell";
UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
// allimageArray has the Assest URL fo the images
NSURL *aURL=[[NSURL alloc]initWithString:[NSString stringWithFormat:@"%@",[allImageArray objectAtIndex:indexPath.row]]];
[assestLibrary assetForURL:aURL resultBlock:^(ALAsset *asset)
 {
     UIImage  *copyOfOriginalImager = [UIImage imageWithCGImage:[[asset defaultRepresentation] fullScreenImage] scale:0.5 orientation:UIImageOrientationUp];
     UIImageView*imageView=[[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 90, 90)];
     NSData *imageData;
     imageData=UIImageJPEGRepresentation(copyOfOriginalImager, 0.4);
     [imageView setImage:[UIImage imageWithData:imageData]];
  [cell.contentView addSubview:imageView];
  }
        failureBlock:^(NSError *error)
  {
     // error handling
     NSLog(@"failure-----");
    }];
  return cell;
  }

I am facing many problems in iOS 7 , app crash due to memory pressure , please explain that too