diff --git a/src/main/scala/lc/LabelCaptcha.scala b/src/main/scala/lc/LabelCaptcha.scala
index b491f43..9757051 100644
--- a/src/main/scala/lc/LabelCaptcha.scala
+++ b/src/main/scala/lc/LabelCaptcha.scala
@@ -18,17 +18,28 @@ class LabelCaptcha extends ChallengeProvider {
       unknownAnswers += file -> Map[String, Int]()
       total += file -> 0
   }
+
   def getId = "LabelCaptcha"
+
   def returnChallenge(): Challenge = synchronized {
     val r = scala.util.Random.nextInt(knownFiles.length)
     val s = scala.util.Random.nextInt(unknownFiles.length)
     val knownImageFile = knownFiles(r)
     val unknownImageFile = unknownFiles(s)
     val ip = new ImagePair(knownImageFile, unknownImageFile)
-    val token = scala.util.Random.nextInt(10000).toString
-    tokenImagePair += (token -> ip)
+
     var knownImage = ImageIO.read(new File("known/"+knownImageFile))
     var unknownImage = ImageIO.read(new File("unknown/"+unknownImageFile))
+    val mergedImage = merge(knownImage, unknownImage)
+
+    val token = encrypt(knownImageFile + "," + unknownImageFile)
+    val baos = new ByteArrayOutputStream()
+    ImageIO.write(mergedImage,"png",baos)
+
+    new Challenge(baos.toByteArray(), "image/png", token)
+  }
+
+  private def merge(knownImage: BufferedImage, unknownImage: BufferedImage) = {
     val width = knownImage.getWidth()+unknownImage.getWidth()
     val height = List(knownImage.getHeight(), unknownImage.getHeight()).max
     val imageType = knownImage.getType()
@@ -39,16 +50,17 @@ class LabelCaptcha extends ChallengeProvider {
     g.drawImage(knownImage, null, 0, 0)
     g.drawImage(unknownImage, null, knownImage.getWidth(), 0)
     g.dispose()
-    val baos = new ByteArrayOutputStream()
-    ImageIO.write(finalImage,"png",baos)
-    new Challenge(baos.toByteArray(), "image/png", token)
+    finalImage
   }
+
   def checkAnswer(token: String, input: String): Boolean = synchronized {
-    val imagePair = tokenImagePair(token)
-    val expectedAnswer = imagePair.known.split('.')(0)
+    val parts = decrypt(token).split(",")
+    val knownImage = parts(0)
+    val unknownImage = parts(1)
+    val expectedAnswer = knownImage.split('.')(0)
     val userAnswer = input.split(' ')
     if(userAnswer(0)==expectedAnswer) {
-      val unknownFile = tokenImagePair(token).unknown
+      val unknownFile = unknownImage
       if((unknownAnswers(unknownFile)).contains(userAnswer(1))) {
         unknownAnswers(unknownFile)(userAnswer(1)) += 1
         total(unknownFile) += 1
@@ -69,6 +81,12 @@ class LabelCaptcha extends ChallengeProvider {
       false
     }
   }
+
+  // TODO: Encryption is not implemented for the POC, since the API re-maps the tokens anyway.
+  //       But we need to encrypt after POC, to avoid leaking file-names.
+  //       There are good ideas here: https://stackoverflow.com/questions/1205135/how-to-encrypt-string-in-java
+  private def encrypt(s: String) = s
+  private def decrypt(s: String) = s
 }
 
 class ImagePair(val known: String, val unknown: String)