Image prediction using trained model (#2392)

* Image prediction using trained model
* Inference on custom images
* Updated the PR following the PEP8 guidelines and made the requested changes
---------
Co-authored-by: Svetlana Karslioglu <svekars@fb.com>

beginner_source/transfer_learning_tutorial.py

@@ -44,6 +44,7 @@
 import matplotlib.pyplot as plt
 import time
 import os
+from PIL import Image
 from tempfile import TemporaryDirectory
 
 cudnn.benchmark = True
@@ -337,6 +338,47 @@ def visualize_model(model, num_images=6):
 plt.ioff()
 plt.show()
 
+
+######################################################################
+# Inference on custom images
+# --------------------------
+#
+# Use the trained model to make predictions on custom images and visualize
+# the predicted class labels along with the images.
+#
+
+def visualize_model_predictions(model,img_path):
+    was_training = model.training
+    model.eval()
+
+    img = Image.open(img_path)
+    img = data_transforms['val'](img)
+    img = img.unsqueeze(0)
+    img = img.to(device)
+
+    with torch.no_grad():
+        outputs = model(img)
+        _, preds = torch.max(outputs, 1)
+
+        ax = plt.subplot(2,2,1)
+        ax.axis('off')
+        ax.set_title(f'Predicted: {class_names[preds[0]]}')
+        imshow(img.cpu().data[0])
+
+        model.train(mode=was_training)
+
+######################################################################
+#
+
+visualize_model_predictions(
+    model_conv,
+    img_path='data/hymenoptera_data/val/bees/72100438_73de9f17af.jpg'
+)
+
+plt.ioff()
+plt.show()
+
+
 ######################################################################
 # Further Learning
 # -----------------