Waits until the end of the frame after all cameras and GUI is rendered, just before displaying the frame on screen.

You can use it to read the display into a texture, encode it as an image file (see Texture2D.ReadPixels and Texture2D.EncodeToPNG) and send it somewhere.

yield new WaitForEndOfFrame ();

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    IEnumerator Example() {
        yield return new WaitForEndOfFrame();
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Example() as IEnumerator:
		yield WaitForEndOfFrame()

Another example:

// Saves screenshot as PNG file.
import System.IO;
// Take a shot immediately
function Start() {
	UploadPNG();
}
function UploadPNG() {
	// We should only read the screen buffer after rendering is complete
	yield WaitForEndOfFrame();
	// Create a texture the size of the screen, RGB24 format
	var width = Screen.width;
	var height = Screen.height;
	var tex = new Texture2D( width, height, TextureFormat.RGB24, false );
	// Read screen contents into the texture
	tex.ReadPixels( Rect(0, 0, width, height), 0, 0 );
	tex.Apply();
	// Encode texture into PNG
	var bytes = tex.EncodeToPNG();
	Destroy( tex );
	// For testing purposes, also write to a file in the project folder
	// File.WriteAllBytes(Application.dataPath + "/../SavedScreen.png", bytes);

	// Create a Web Form
	var form = new WWWForm();
	form.AddField("frameCount", Time.frameCount.ToString());
	form.AddBinaryData("fileUpload",bytes);
	// Upload to a cgi script
	var w = WWW("http:/localhostcgi-bin/env.cgi?post", form);
	yield w;
	if (w.error != null)
		print(w.error);
	else
		print("Finished Uploading Screenshot");
}

using System.IO;
using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Start() {
        UploadPNG();
    }
    IEnumerator UploadPNG() {
        yield return new WaitForEndOfFrame();
        int width = Screen.width;
        int height = Screen.height;
        Texture2D tex = new Texture2D(width, height, TextureFormat.RGB24, false);
        tex.ReadPixels(new Rect(0, 0, width, height), 0, 0);
        tex.Apply();
        byte[] bytes = tex.EncodeToPNG();
        Destroy(tex);
        WWWForm form = new WWWForm();
        form.AddField("frameCount", Time.frameCount.ToString());
        form.AddBinaryData("fileUpload", bytes);
        WWW w = new WWW("http:/localhostcgi-bin/env.cgi?post", form);
        yield return w;
        if (w.error != null)
            print(w.error);
        else
            print("Finished Uploading Screenshot");
    }
}

import System.IO
import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Start() as void:
		UploadPNG()

	def UploadPNG() as IEnumerator:
		yield WaitForEndOfFrame()
		width as int = Screen.width
		height as int = Screen.height
		tex as Texture2D = Texture2D(width, height, TextureFormat.RGB24, false)
		tex.ReadPixels(Rect(0, 0, width, height), 0, 0)
		tex.Apply()
		bytes as (byte) = tex.EncodeToPNG()
		Destroy(tex)
		form as WWWForm = WWWForm()
		form.AddField('frameCount', Time.frameCount.ToString())
		form.AddBinaryData('fileUpload', bytes)
		w as WWW = WWW('http:/localhostcgi-bin/env.cgi?post', form)
		yield w
		if w.error != null:
			print(w.error)
		else:
			print('Finished Uploading Screenshot')

// Shows alpha channel contents in the game view.
private var mat : Material;
// After the frame is completely rendered, we'll
// draw a full screen quad that extracts the alpha channel.
function Start() {
	while (true) {
		yield WaitForEndOfFrame();
		if( !mat ) {
			mat = new Material( "Shader \"Hidden/Alpha\" {" +
				"SubShader {" +
				"    Pass {" +
				"        ZTest Always Cull Off ZWrite Off" +
				"        Blend DstAlpha Zero" +
				"        Color (1,1,1,1)" +
				"    }" +
				"}" +
				"}"
			);
		}
		GL.PushMatrix ();
		GL.LoadOrtho ();
		for (var i = 0; i < mat.passCount; ++i) {
			mat.SetPass (i);
			GL.Begin( GL.QUADS );
			GL.Vertex3( 0, 0, 0.1 );
			GL.Vertex3( 1, 0, 0.1 );
			GL.Vertex3( 1, 1, 0.1 );
			GL.Vertex3( 0, 1, 0.1 );
			GL.End();
		}
		GL.PopMatrix ();
	}
}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    private Material mat;
    IEnumerator Start() {
        while (true) {
            yield return new WaitForEndOfFrame();
            if (!mat)
                mat = new Material("Shader \"Hidden/Alpha\" {" + "SubShader {" + "    Pass {" + "        ZTest Always Cull Off ZWrite Off" + "        Blend DstAlpha Zero" + "        Color (1,1,1,1)" + "    }" + "}" + "}");
            
            GL.PushMatrix();
            GL.LoadOrtho();
            int i = 0;
            while (i < mat.passCount) {
                mat.SetPass(i);
                GL.Begin(GL.QUADS);
                GL.Vertex3(0, 0, 0.1F);
                GL.Vertex3(1, 0, 0.1F);
                GL.Vertex3(1, 1, 0.1F);
                GL.Vertex3(0, 1, 0.1F);
                GL.End();
                ++i;
            }
            GL.PopMatrix();
        }
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	private mat as Material

	def Start() as IEnumerator:
		while true:
			yield WaitForEndOfFrame()
			if not mat:
				mat = Material((((((((('Shader "Hidden/Alpha" {' + 'SubShader {') + '    Pass {') + '        ZTest Always Cull Off ZWrite Off') + '        Blend DstAlpha Zero') + '        Color (1,1,1,1)') + '    }') + '}') + '}'))
			GL.PushMatrix()
			GL.LoadOrtho()
			i as int = 0
			while i < mat.passCount:
				mat.SetPass(i)
				GL.Begin(GL.QUADS)
				GL.Vertex3(0, 0, 0.1F)
				GL.Vertex3(1, 0, 0.1F)
				GL.Vertex3(1, 1, 0.1F)
				GL.Vertex3(0, 1, 0.1F)
				GL.End()
				++i
			GL.PopMatrix()