Dude,as per my understanding..only the image name is stored in the database but the imageurl.So only with the image name you cannot get the image from database.Also bind the image path to the Imageurl as shown below.
ImageUrl='<%# String.Format("~/path/to/image/" + Eval("product_img")) %>'
Replace ~/path/to/image/ with the path where the images are stored.
---Prathap.