Domino

After cataloging all tiles in the standard double-six set (containing 28 tiles), I checked for each possible pair: [0,0], [0,1], [0,2], [0,3], [0,4], [0,5], [0,6], [1,1], [1,2], [1,3], [1,4], [1,5], [1,6], [2,2], [2,3], [2,4], [2,5], [2,6], [3,3], [3,4], [3,5], [3,6], [4,4], [4,5], [4,6], [5,5], [5,6], [6,6]. The tile [1, 6] (or [6, 1]) is the only one not present in the image.

The excluded domino is number 2 and 1

By systematically checking all possible domino combinations from 0-6, the domino [0, 1] is not present in the image. The standard double-six set contains 28 tiles representing all unique pairs: [0,0] through [6,6]. After identifying all 27 visible dominoes, [0, 1] is the missing tile.

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After identifying and counting the visible tiles from the image and comparing to a complete double-six set, the double-six tile (6-6) is the only one not present.

In a standard double-six domino set, each number (0-6) appears exactly 8 times across all 28 tiles. By counting the occurrences of each number in the image: 0 appears 8 times, 1 appears 8 times, 2 appears 8 times, 3 appears 8 times, 6 appears 8 times, but both 4 and 5 appear only 7 times each. The only domino that contains both 4 and 5 is [4,5]. All other dominoes involving 4 ([0,4], [1,4], [2,4], [3,4], [4,4], [4,6]) are visible in the image, and all other dominoes involving 5 ([0,5], [1,5], [2,5], [3,5], [5,5], [5,6]) are also visible.