Hi Mastafa
As we know right from content type we can determine the file type and operating system sets the icon for it, but its out of box to do the same in asp.net, i can give you an alternative idea to save all images in your folder, so as many type of images exists or different type of file type exists as many type of images you would be having, rename those images with extention of your file so say for example for your .doc file the image would be doc.png for .pdf the name would be pdf.png
so now just get the extention of corresponding file and get that image from image directory
let me know
Thanks