Can anyone tell me how can i calculate noise in an image when i do not have the original image(image without noise) ?
It depends on the definition of noise for your specefic problem.
If you want to detect a red traffic light, all non-red pixels are noise. If you want to control the quality of your camera-sensor at low light and take a photo of a B/W-checkerboard, all non-white and non-black pixels are noise. If you want to assess the thermal noise of a camera-sensor by taking a photo with a covered lense, all non-black pixels are noise. On a photo of the sky, all clouds can be noise, or the searched signal. If you are looking for high-frequency values, all low-frequency signals are noise - and vice-versa.
Therefore you have to define "noise" at first, before you can determine its amount. Finally you can measure the noise for each pixel, each region, each intensity, each contrast relation or as mean/max/median for the whole image.
Summary: Please explain the details.