Application.CaptureScreenshot
static function CaptureScreenshot(filename: string, superSize: int = 0): void;
static void CaptureScreenshot(string filename, int superSize = 0);
static def CaptureScreenshot(filename as string, superSize as int = 0) as void
Parameters

filename Pathname to save the screenshot file to.
superSize Factor by which to increase resolution.
Description

Captures a screenshot at path filename as a PNG file.

If the file exists already, it will be overwritten. This function does nothing if used from inside the web player. On mobile platforms the filename is appended to the persistent data path.

When superSize parameter is larger than 1, a larger resolution screenshot will be produced. For example, passing 4 will make the screenshot be 4x4 larger than it normally would. This is useful to produce screenshots for printing.
	function OnMouseDown() {
		Application.CaptureScreenshot("Screenshot.png");
	}
using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnMouseDown() {
        Application.CaptureScreenshot("Screenshot.png");
    }
}
import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnMouseDown() as void:
		Application.CaptureScreenshot('Screenshot.png')