Processing Image Saving

import java.security.*;
import java.util.*;

static class Utils {
  static void saveImage(PApplet applet) {
    int i = 0;
    File file = null;
    String fileName = null;
    do {
      i++;
      fileName = "Iteration " + i + ".png";
      file = new File(applet.sketchPath(fileName));
    } 
    while (file.exists());
    applet.save(fileName);

    if (i == 1) return; //This is the first image we've saved.

    //Check to make sure that this image is not identical to the last.
    byte[] thisFileChecksum = Utils.checksum(file);
    byte[] lastFileChecksum = Utils.checksum(new File(applet.sketchPath("Iteration " + (i - 1) + ".png")));
    if (thisFileChecksum != null && lastFileChecksum != null && Arrays.equals(thisFileChecksum, lastFileChecksum)) {
      file.delete();
    }
  }

  //Adapted from http://www.mkyong.com/java/how-to-generate-a-file-checksum-value-in-java/
  static byte[] checksum(File file) {
    try {
      MessageDigest md = MessageDigest.getInstance("MD5");
      FileInputStream fis = new FileInputStream(file);
      byte[] dataBytes = new byte[1024];

      int nread = 0; 

      while ( (nread = fis.read (dataBytes)) != -1) {
        md.update(dataBytes, 0, nread);
      }
      byte[] digest = md.digest(); 
      return digest;
    }
    finally {
      return null;
    }
  }
}