Android : Why does it take different amount of time to download images that have the same size from Flickr?

I have an Android app that downloads images from Flickr. I use HttpUrlConnection to download from URL, and BitmapFactory.decodeStream() to create a bitmap. I don't know why some images take longer to download than others, even though they have the same sizes. Is it because they are on different servers? Please help me answer this. Thanks everyone.