Domino

By cataloging all 27 dominoes shown in the image and comparing them against the standard double-six set of 28 tiles, the [6, 6] tile is the only one missing.

By systematically cataloging all 27 visible dominoes in the image and comparing against the complete set of 28 unique dominoes in a standard double-six set, the domino [0, 1] is the only one not present. All other combinations from [0,0] through [6,6] are accounted for in the image.

The domino [0, 0] is missing from the image

Let me systematically identify all dominoes in the image and find which one is missing from a standard double-six set. A standard set has 28 tiles. The image shows 27 tiles. Going through each visible domino and checking against the complete set of 28 combinations, the [0,0] blank-blank domino appears to be missing.

The double-six tile (6,6) is not present among the 27 displayed dominoes; every other domino from the double-six set appears to be shown.

The image displays a collection of dominoes from a standard double-six set (28 total dominoes). By examining the arrangement and identifying the present dominoes—including [0|0] in the top row, [1|1] in the middle rows, and [5|5] in the bottom row along with various non-double combinations—the double-two [2|2] is the only double that is conspicuously absent from the complete set. All other dominoes required to complete the full sequence appear to be present in the pattern, making [2|2] the excluded domino.