Download Large size (in Mb) Images from CQ

HI , 

At present, I use the url path to the Image to download the image using HttpWebRequest/webclient in c# , asp.net

If the image size is large, it takes a lot of time to download the image, and for images with low size, the download time is less.

Is there any way to download large images with in a short time and in thumbnail format?

I use,

string strImageURL = http://localhost:4502/content/dataservices-samples/images/adep_appicon_128.png

 MemoryStream smImageStream = new MemoryStream(new System.Net.WebClient().DownloadData(strImageURL));
 using (SD.Bitmap loBMP = new SD.Bitmap(smImageStream))
    {

    //resize to thumbnail size(120X120) for preview

   }

I am looking for something like 

string strImageURL = http://localhost:4502/content/dataservices-samples/images/adep_appicon_128.thumb, so as to get the thumbnail version of the same image,

The images are not placed in dam, but another folder and only one version of image is available there.

any suggestions is appreciated