Bundle IDからアプリのアイコンを取得する ref: http://qiita.com/ykst@github/items/ffc09fee78483d04b571

BundleHelper.m

@interface BundleHelper : NSObject
+ (void)retrieveIconURLForBundleID:(NSString *)bundle_id withHandler:(void (^)(NSURL *url))handler;
@end

@implementation BundleHelper
+ (void)retrieveIconURLForBundleID:(NSString *)bundle_id withHandler:(void (^)(NSURL *))handler
{
    // カレントロケールからストアの国を推定
    static NSString *country;
    NSLocale *currentLocale = [NSLocale currentLocale];
    country = [currentLocale objectForKey:NSLocaleCountryCode];

    // Search APIを叩く => http://itunes.apple.com/<country code>/lookup?bundleID=<bundle id>
    NSMutableString *requestUrlString = [[NSMutableString alloc] init];
    [requestUrlString appendFormat:@"http://itunes.apple.com/%@/lookup", country];
    [requestUrlString appendFormat:@"?bundleId=%@", bundle_id];

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:requestUrlString]];
    [request setTimeoutInterval:20.0f];
    [request setCachePolicy:NSURLRequestReturnCacheDataElseLoad];

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    // 非同期リクエスト (キューはいいかげん)
    [NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        if (!connectionError) {
            // APIレスポンスのJSONデコード
            NSError *jsonError = nil;
            NSDictionary *jsonDictionary = [NSJSONSerialization JSONObjectWithData:data
                                                                           options:NSJSONReadingMutableLeaves
                                                                             error:&jsonError];
            if (!jsonError) {
                NSArray *results = [jsonDictionary objectForKey:@"results"];
                if (results.count > 0) {
                    // 検索結果の一つ目を取得
                    NSDictionary *dic = results[0];
                    app.dic = dic;
                    // 60x60のアイコンのURL
                    handler([NSURL URLWithString:[dic objectForKey:@"artworkUrl60"]]);
                    });
                } else {
                    handler(nil);
                }
            } else {
                handler(nil);
            }
        } else {
            handler(nil);
        }
    }];
}
@end