Output the diff image along with the original images for easy comparison.

nodejs-tests/compareImages.test.js

@@ -21,6 +21,12 @@ describe('compareImages', () => {
     );
 
     expect(buffer.equals(comparison)).toBe(true);
+
+    const buffer2 = data.getBuffer(true);
+    const comparison2 = fs.readFileSync(
+      './nodejs-tests/PeopleComparedToPeople2WithOriginal.png'
+    );
+    expect(buffer2.equals(comparison2)).toBe(true);
   });
 
   test('throws when failed', async () => {

resemble.js

@@ -513,8 +513,16 @@ URL: https://github.com/Huddle/Resemble.js
 			};
 
 			if (hiddenCanvas.toBuffer) {
-				data.getBuffer = function() {
+				data.getBuffer = function(includeOriginal) {
-					context.putImageData(imgd, 0, 0);
+					if (includeOriginal) {
+						var imageWidth = hiddenCanvas.width + 2;
+						hiddenCanvas.width = imageWidth * 3;
+						context.putImageData(img1, 0, 0);
+						context.putImageData(img2, imageWidth, 0);
+						context.putImageData(imgd, imageWidth * 2, 0);
+					} else {
+						context.putImageData(imgd, 0, 0);
+					}
 					return hiddenCanvas.toBuffer();
 				}
 			}