# Spot the differences

Once a month, or once every other month, I try to take a more in depth look at a puzzle type. This month I want to have a look at the “spot the differences” puzzles. This is a pretty popular type of puzzle, Bing turns up at least 4 different websites and the google playstore has at least 10 apps. URLs of the websites are mentioned at the end of this article. The trigger for this post is my recent acquisition of a magazine “zoek de verschillen” (find the differences) by Denksport, the largest puzzle publisher in the Netherlands.

1) Spot the differences

Try to find all 15 differences!
(The picture has been taken in the Netherlands, in the tourist town of Vaals).

You can check your solutions here

While making this puzzle, trying my hand at some of the puzzles in the magazine, and browsing around on the web, I noticed there are several types of changes:
1 – an object appears in one image and not in the other. An example is a traffic sign that has an arrow in one image and no arrow in the other. The object often is small.
2 – the object is present in both images, but with different colors. For instance, if you have a dish with colorful sweets, one of the sweets has been changed from green to orange.
3 – the object is present in both images, but in one image it is longer, shorter, wider or narrower than in the other. In one of the puzzles in the web, I noticed a garbage can, attached to a pole, reached to the pavement on the left imgae while in the right image it was a foot above the pavement.
4 – the object is present in both images, and the object is identical in both images, but in a different spot. For example, that crow on the roof is sitting near one end of the roof or in the middle.

What makes a puzzle tough? Which differences are hard to spot? I could not find any scientific research on this topic. Generally, I’d say that small differences are harder to spot than big differences. But some differences seem to be ignored by the eye or mind, even though they are not particularly small. A change in a background is often harder to spot than one in the foreground. Changes to the top of an object seem to be spotted more easily than changes to the bottom.

2 identicals
A second format that the afore mentioned magazine applies is that of 6 copies, and you have to find the 2 identical copies.

The abundant availability of digital photos has greatly enhanced the possibility for everyone, both amateur and professional, to create these puzzles. I don’t have photoshop, but MS paint served me well during the creation of the puzzles above. Before the age of electronic manipulation, the images were often handdrawn. You can find one on the english language wikipedia.

You can check your solutions here

3) Subdivisions
A large photo is subidivided into small rectangles, with rows and column labelled. A few of the rectangles are copied below the photo and the puzzler has to find out which small rectangle they correspond with.

What are the coordinates of the two cut outs?

You can check your solutions here

4) Cutout
A rectangle is cut out from a photo and displayed below it. Several other sections are copied below the photo, and the puzzler has to find out which is the cut out which fits into the picture. The cut outs are tilted, and I currently lack the skills or tools to do this for you.