diff --git a/openbr/gui/classifier.cpp b/openbr/gui/classifier.cpp
index 6e72c59..3f60ac0 100644
--- a/openbr/gui/classifier.cpp
+++ b/openbr/gui/classifier.cpp
@@ -7,7 +7,7 @@ using namespace br;
 
 /**** CLASSIFIER ****/
 /*** PUBLIC ***/
-Classifier::Classifier(QWidget *parent)
+GUIClassifier::GUIClassifier(QWidget *parent)
     : QLabel(parent)
 {
     setAlignment(Qt::AlignCenter);
@@ -15,26 +15,26 @@ Classifier::Classifier(QWidget *parent)
     connect(this, SIGNAL(newClassification(QString,QString)), this, SLOT(setClassification(QString,QString)));
 }
 
-void Classifier::setAlgorithm(const QString &algorithm)
+void GUIClassifier::setAlgorithm(const QString &algorithm)
 {
     this->algorithm = algorithm;
 }
 
 /*** PUBLIC SLOTS ***/
-void Classifier::classify(const File &file)
+void GUIClassifier::classify(const File &file)
 {
-    QtConcurrent::run(this, &Classifier::_classify, file);
+    QtConcurrent::run(this, &GUIClassifier::_classify, file);
 }
 
 /*** PRIVATE SLOTS ***/
-void Classifier::setClassification(const QString &key, const QString &value)
+void GUIClassifier::setClassification(const QString &key, const QString &value)
 {
     if (key.isEmpty()) clear();
     else               setText(QString("%1: <b>%2</b>").arg(key, value));
 }
 
 /*** PRIVATE ***/
-void Classifier::_classify(File file)
+void GUIClassifier::_classify(File file)
 {
     QString key, value;
     QSharedPointer<Transform> transform = Transform::fromAlgorithm(algorithm);
diff --git a/openbr/gui/classifier.h b/openbr/gui/classifier.h
index 02a8c3d..eff1463 100644
--- a/openbr/gui/classifier.h
+++ b/openbr/gui/classifier.h
@@ -1,5 +1,5 @@
-#ifndef BR_CLASSIFIER_H
-#define BR_CLASSIFIER_H
+#ifndef BR_GUICLASSIFIER_H
+#define BR_GUICLASSIFIER_H
 
 #include <QLabel>
 #include <QWidget>
@@ -9,13 +9,13 @@
 namespace br
 {
 
-class BR_EXPORT Classifier : public QLabel
+class BR_EXPORT GUIClassifier : public QLabel
 {
     Q_OBJECT
     QString algorithm;
 
 public:
-    explicit Classifier(QWidget *parent = 0);
+    explicit GUIClassifier(QWidget *parent = 0);
     void setAlgorithm(const QString &algorithm);
 
 public slots:
@@ -33,4 +33,4 @@ signals:
 
 } // namespace br
 
-#endif // BR_CLASSIFIER_H
+#endif // BR_GUICLASSIFIER_H
diff --git a/openbr/gui/templatemetadata.cpp b/openbr/gui/templatemetadata.cpp
index 06d39cf..e15c758 100644
--- a/openbr/gui/templatemetadata.cpp
+++ b/openbr/gui/templatemetadata.cpp
@@ -21,7 +21,7 @@ TemplateMetadata::TemplateMetadata(QWidget *parent)
 
 void TemplateMetadata::addClassifier(const QString &classifier_, const QString algorithm)
 {
-    QSharedPointer<Classifier> classifier(new Classifier());
+    QSharedPointer<GUIClassifier> classifier(new GUIClassifier());
     classifier->setAlgorithm(classifier_);
     layout->addWidget(classifier.data());
     conditionalClassifiers.append(ConditionalClassifier(algorithm, classifier));
diff --git a/openbr/gui/templatemetadata.h b/openbr/gui/templatemetadata.h
index ab6c205..a009861 100644
--- a/openbr/gui/templatemetadata.h
+++ b/openbr/gui/templatemetadata.h
@@ -24,10 +24,10 @@ class BR_EXPORT TemplateMetadata : public QWidget
     struct ConditionalClassifier
     {
         QString algorithm;
-        QSharedPointer<Classifier> classifier;
+        QSharedPointer<GUIClassifier> classifier;
 
         ConditionalClassifier() {}
-        ConditionalClassifier(const QString &algorithm_, const QSharedPointer<Classifier> &classifier_)
+        ConditionalClassifier(const QString &algorithm_, const QSharedPointer<GUIClassifier> &classifier_)
             : algorithm(algorithm_), classifier(classifier_) {}
     };
     QList<ConditionalClassifier> conditionalClassifiers;
diff --git a/openbr/openbr_plugin.h b/openbr/openbr_plugin.h
index da9b8d0..8d0e219 100644
--- a/openbr/openbr_plugin.h
+++ b/openbr/openbr_plugin.h
@@ -1383,8 +1383,8 @@ class BR_EXPORT Representation : public Object
 public:
     virtual ~Representation() {}
 
-    virtual cv::Mat init(cv::Mat &image) const;
-    virtual QList<float> evaluate(const cv::Mat &image, const QList<int> &indices) const;
+    virtual cv::Mat preprocess(cv::Mat &image) const { return image; }
+    virtual QList<float> evaluate(const cv::Mat &image, const QList<int> &indices) const = 0;
 };
 
 class BR_EXPORT Classifier : public Object
@@ -1394,8 +1394,8 @@ class BR_EXPORT Classifier : public Object
 public:
     virtual ~Classifier() {}
 
-    virtual void train(const QList<cv::Mat> &images, const QList<int> &labels);
-    virtual float classify(const QList<cv::Mat> &image) const;
+    virtual void train(const QList<cv::Mat> &images, const QList<float> &labels) = 0;
+    virtual float classify(const QList<cv::Mat> &image) const = 0;
 };
 
 /*!