в self.photos вы храните массив json объектов data, но никак не имена файлов на вашем устройстве.
{
"data": [{
"type": "image",
"users_in_photo": [],
"filter": "Earlybird",
"tags": ["snow"],
"comments": {
"data": [{
"created_time": "1296703540",
"text": "Snow",
"from": {
"username": "emohatch",
"username": "Dave",
"id": "1242695"
},
"id": "26589964"
},
{
"created_time": "1296707889",
"text": "#snow",
"from": {
"username": "emohatch",
"username": "Emo Hatch",
"id": "1242695"
},
"id": "26609649"
}],
"count": 3
}
"caption": {
"created_time": "1296703540",
"text": "#Snow",
"from": {
"username": "emohatch",
"id": "1242695"
},
"id": "26589964"
},
"likes": {
"count": 1,
"data": [{
"username": "mikeyk",
"full_name": "Mike Krieger",
"id": "4",
"profile_picture": "http://distillery.s3.amazonaws.com/profiles/profile_1242695_75sq_1293915800.jpg"
}]
},
"link": "http://instagr.am/p/BWl6P/",
"user": {
"username": "emohatch",
"profile_picture": "http://distillery.s3.amazonaws.com/profiles/profile_1242695_75sq_1293915800.jpg",
"id": "1242695",
"full_name": "Dave"
},
"created_time": "1296703536",
"images": {
"low_resolution": {
"url": "http://distillery.s3.amazonaws.com/media/2011/02/02/f9443f3443484c40b4792fa7c76214d5_6.jpg",
"width": 306,
"height": 306
},
"thumbnail": {
"url": "http://distillery.s3.amazonaws.com/media/2011/02/02/f9443f3443484c40b4792fa7c76214d5_5.jpg",
"width": 150,
"height": 150
},
"standard_resolution": {
"url": "http://distillery.s3.amazonaws.com/media/2011/02/02/f9443f3443484c40b4792fa7c76214d5_7.jpg",
"width": 612,
"height": 612
}
},
"id": "22699663",
"location": null
},
...]
}
А вам нужна ссылка на файл, либо сам файл
"images": {
"low_resolution": {
"url": "http://distillery.s3.amazonaws.com/media/2011/02/02/f9443f3443484c40b4792fa7c76214d5_6.jpg",
"width": 306,
"height": 306
},
"thumbnail": {
"url": "http://distillery.s3.amazonaws.com/media/2011/02/02/f9443f3443484c40b4792fa7c76214d5_5.jpg",
"width": 150,
"height": 150
},
"standard_resolution": {
"url": "http://distillery.s3.amazonaws.com/media/2011/02/02/f9443f3443484c40b4792fa7c76214d5_7.jpg",
"width": 612,
"height": 612
}
},
надо загрузить картинку в каждую ячейку
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];
NSString *url = [self.photos objectAtIndex:indexPath.row][@"images"][@"thumbnail"][@"url"];
UIImageView *recipeImageView = (UIImageView *)[cell viewWithTag:100];
recipeImageView.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:url]]];
return cell;
}
А вообще лучше загружать асинхронно =)
А еще лучше можно глянуть в сторону
InstagramKit 
