diff --git a/bus_analyzer/bus_analyzer/extract.py b/bus_analyzer/bus_analyzer/extract.py
index 9da601a..cb5a20f 100644
--- a/bus_analyzer/bus_analyzer/extract.py
+++ b/bus_analyzer/bus_analyzer/extract.py
@@ -129,7 +129,7 @@ def normalize(image):
 	return image
 
 
-def recognize_digit(prototypes, image, blank_is_zero=False):
+def recognize_digit(prototypes, image, blank_is_zero=False, mask=None):
 	"""Takes a normalized digit image and returns (detected number, score, all_scores)
 	where score is between 0 and 1. Higher numbers are more certain the number is correct.
 	all_scores is for debugging.
@@ -143,7 +143,7 @@ def recognize_digit(prototypes, image, blank_is_zero=False):
 		except ValueError:
 			return None
 	scores = sorted([
-		(compare_images(prototype, image), maybeFloat(n))
+		(compare_images(prototype, image, mask), maybeFloat(n))
 		for n, prototype in prototypes.items()
 	], reverse=True)
 	best_score, number = scores[0]
@@ -153,10 +153,16 @@ def recognize_digit(prototypes, image, blank_is_zero=False):
 	return number, best_score - runner_up_score, scores
 
 
-def compare_images(prototype, image):
+def compare_images(prototype, image, mask=None):
 	"""Takes a normalized digit image and a prototype image, and returns a score
 	for how close the image is to looking like that prototype."""
-	pairs = zip(image.getdata(), prototype.getdata())
+	image = list(image.getdata())
+	prototype = list(prototype.getdata())
+	if mask:
+		mask = list(mask.getdata())
+		image = [mask[i] / 255 * image[i] for i in range(len(mask))]
+		prototype = [mask[i] / 255 * prototype[i] for i in range(len(mask))]
+	pairs = zip(image, prototype)
 	error_squared = sum((a - b)**2 for a, b in pairs)
 	MAX_ERROR_SQUARED = 255**2 * len(pairs)
 	return 1 - (float(error_squared) / MAX_ERROR_SQUARED)**0.5
@@ -195,8 +201,9 @@ def recognize_odometer(prototypes, frame):
 	"""
 	odo = frame.crop(AREA_COORDS["odo"])
 	digits = extract_digits(odo, "odo")
+	mask = Image.open(prototypes['mask'][0])
 	digits = [
-		recognize_digit(prototypes["odo-digits"], digit) for digit in digits[:-1]
+		recognize_digit(prototypes["odo-digits"], digit, mask=mask) for digit in digits[:-1]
 	] + [
 		recognize_digit(prototypes["odo-last-digit"], digits[-1])
 	]
@@ -213,8 +220,9 @@ def recognize_odometer(prototypes, frame):
 def recognize_clock(prototypes, frame):
 	clock = frame.crop(AREA_COORDS["clock"])
 	digits = extract_digits(clock, "clock")
+	mask = Image.open(prototypes['mask'][0])
 	digits = [
-		recognize_digit(prototypes["odo-digits"], digit, i == 0) for i, digit in enumerate(digits)
+		recognize_digit(prototypes["odo-digits"], digit, i == 0, mask=mask) for i, digit in enumerate(digits)
 	]
 	if any(digit is None for digit, _, _ in digits):
 		# If any digit is None, report whole thing as None
diff --git a/bus_analyzer/prototypes/mask/mask.png b/bus_analyzer/prototypes/mask/mask.png
new file mode 100644
index 0000000..6bde809
Binary files /dev/null and b/bus_analyzer/prototypes/mask/mask.png differ