extract all used images from unity project to a destination folder. http://answers.unity3d.com/questions/57909/find-unused-assets-in-project.html

AssetExtractor.cs

using UnityEngine;
using UnityEditor;
using System;
using System.IO;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

public class AssetExtractor : EditorWindow {
	Vector2 scrollPos;
	List<string> usedFileNames;
	string destinationFolder = "";

	[MenuItem ("Window/Asset Extractor")]
	public static void  ShowWindow () {
		EditorWindow.GetWindow(typeof(AssetExtractor));
	}

	void OnGUI(){
		if(GUILayout.Button("Fill list from editor log")){
			usedFileNames = parseUsedAssetsFromLog();
		}
		if(GUILayout.Button("Clear editor log")){
			File.WriteAllText(getEditorLogFilePath(), string.Empty);
		}

		if(usedFileNames != null){
			var usedImageFiles =
				from file in usedFileNames 
				where isImageFile(file) 
				select file;
	
			if(GUILayout.Button("Write files to folder")){
				destinationFolder = EditorUtility.OpenFolderPanel("Select folder", destinationFolder, "");
				Debug.Log(destinationFolder);
				if(!String.IsNullOrEmpty(destinationFolder)){
					foreach(string path in usedImageFiles){
						//Debug.Log("copy " + path + " to " + destinationFolder + Path.GetFileName(path));
						Directory.CreateDirectory(Path.GetDirectoryName(Path.Combine(destinationFolder, path)));
						File.Copy(Path.Combine(Application.dataPath, path), Path.Combine(destinationFolder, path), true);
					}
				}
			}
			scrollPos = EditorGUILayout.BeginScrollView(scrollPos);
	
			foreach(string path in usedImageFiles){
				//GUILayout.Label(filename);
				GUILayout.Label(Path.Combine(Application.dataPath, path) + " -> " + Path.Combine(destinationFolder, path));
			}
			EditorGUILayout.EndScrollView();
		}
	}

	private bool isImageFile(string filepath){
		return filepath.EndsWith(".png")
			|| filepath.EndsWith(".psd")
			|| filepath.EndsWith(".jpg")
			|| filepath.EndsWith(".jpeg");
	}

	private string getEditorLogFilePath(){
		if(Application.platform == RuntimePlatform.OSXEditor){
			string home = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
			return home + "/Library/Logs/Unity/Editor.log";
			//return Path.Combine(home, "/Library/Logs/Unity/Editor.log");
		}
		else if(Application.platform == RuntimePlatform.WindowsEditor){
			string localAppData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
			return Path.Combine(localAppData, @"Unity\Editor\Editor.log");
		}
		return null;
	}

	private List<string> parseUsedAssetsFromLog()
	{
		Debug.Log("parsing file");
		List<string> result = new List<string>();

		string logfilePath = getEditorLogFilePath();
		try
		{
			// Have to use FileStream to get around sharing violations!
			FileStream FS = new FileStream(logfilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
			StreamReader SR = new StreamReader(FS);
			
			string line;
			while (!SR.EndOfStream && !(line = SR.ReadLine()).Contains("Used Assets,"));
			Debug.Log(line);
			while (!SR.EndOfStream && (line = SR.ReadLine()).StartsWith(" "))
			{
				line = line.Substring(line.IndexOf("% ") + 2);
				if(line.StartsWith("Assets/")){
					line = line.Substring(7);
					result.Add(line);
				}
			}
		}
		catch (Exception e)
		{
			Debug.LogException(e);
		}
		return result;
	}
}