I haven't received any answers but after trying different things, i was able to solve this issue. I am answering my own question now so that if anyone faces the same issue, they can solve this problem without wasting much time as i did.
In didStartElement method of NSXMLParser, i wrote the following:
if ([elementName isEqual:@"media:content"])
{
NSString *imageURLString = [attributeDict objectForKey:@"url"];
NSLog(@"imgURL %@",imageURLString);
// Here you can use the imageURLString to download the image
}