diff --git a/sloth/plugins/facedetector.py b/sloth/plugins/facedetector.py
index bf37278..f1a0f9b 100644
--- a/sloth/plugins/facedetector.py
+++ b/sloth/plugins/facedetector.py
@@ -3,42 +3,74 @@ from PyQt4.QtGui import *
 from PyQt4.QtCore import *
 from okapy import BinaryPatternFaceDetector
 
+class Worker(QThread):
+    valueChanged = pyqtSignal(int)
+    def __init__(self, n_images, model, det):
+        QThread.__init__(self)
+        self.n_images = n_images
+        self.model    = model
+        self.det      = det
+        self.canceled = False
+
+    def cancel(self):
+        self.canceled = True
+
+    def run(self):
+        for i in range(self.n_images):
+            index = self.model.index(i, 0)
+            item = self.model.itemFromIndex(index)
+            img = item.data(index, ImageRole)
+            faces = self.det.detectFaces(img)
+            for face in faces:
+                ann = {
+                        'type':       'rect',
+                        'class':      'face',
+                        'x':          face.box.x,
+                        'y':          face.box.y,
+                        'width':      face.box.width,
+                        'height':     face.box.height,
+                        'confidence': face.conf,
+                        }
+                self.model.addAnnotation(index, ann)
+            self.valueChanged.emit(i+1)
+            if self.canceled:
+                return
+
 class FaceDetectorPlugin(QObject):
     def __init__(self, wnd):
         QObject.__init__(self, wnd)
         self.wnd_ = wnd
         self.sc_  = QAction("Detect faces", wnd)
         self.sc_.triggered.connect(self.doit)
+        self.progress = None
+        self.thread   = None
+
+    def on_valueChanged(self, val):
+        if self.progress is not None:
+            self.progress.setValue(val)
+
+    def on_finished(self):
+        self.progress.setValue(self.progress.maximum())
+        self.progress.hide()
+        self.progress = None
+        self.thread   = None
+        self.sc_.setEnabled(True)
 
     def doit(self):
         print "Loading detector..."
         det = BinaryPatternFaceDetector("/cvhci/data/mctcascades/new-detectors/face_frontal_new.xml")
+        self.sc_.setEnabled(False)
         model = self.wnd_.model_
         n_images = model.rowCount()
-        progress = QProgressDialog("Detecting faces...", "Abort", 0, n_images, self.wnd_);
-        progress.setWindowModality(Qt.WindowModal);
-        progress.show()
-
-        for i in range(n_images):
-            index = model.index(i, 0)
-            item = model.itemFromIndex(index)
-            img = item.data(index, ImageRole)
-            faces = det.detectFaces(img)
-            for face in faces:
-                ann = {
-                    'type':       'rect',
-                    'class':      'face',
-                    'x':          face.box.x,
-                    'y':          face.box.y,
-                    'width':      face.box.width,
-                    'height':     face.box.height,
-                    'confidence': face.conf,
-                }
-                model.addAnnotation(index, ann)
-            progress.setValue(i+1);
-            QCoreApplication.processEvents()
-            if progress.wasCanceled():
-                break
+        self.progress = QProgressDialog("Detecting faces...", "Abort", 0, n_images, self.wnd_);
+        self.progress.setWindowModality(Qt.WindowModal)
+        self.progress.show()
+        self.thread = Worker(n_images, model, det)
+        self.progress.canceled.connect(self.thread.cancel)
+        self.thread.finished.connect(self.on_finished)
+        self.thread.valueChanged.connect(self.on_valueChanged)
+        self.thread.start()
+        print "Exiting doit()"
 
     def action(self):
         return self.sc_