Domino

By systematically checking all 28 possible dominoes in a standard double-six set, I identified that the double-four (4|4) is the missing tile. All other dominoes from [0,0] through [6,6], accounting for the symmetry where [i,j] and [j,i] are the same tile, are present in the image.

I systematically went through all 28 dominoes in a standard double-six set and checked them against the image. After carefully counting and identifying each domino present, the tile [0,3] (blank|three) appears to be missing from the set.

After checking for all possible 28 tiles in a double-six set (from [0,0] to [6,6]), the tile with four pips on one side and six pips on the other side is missing from the image.

All other domino pairs 0–6 are present in the image but the double-six tile (6,6) is not visible; therefore the excluded domino is [6,6].

By systematically identifying all 27 dominoes in the image and comparing against the complete set of 28 double-six dominoes, the domino [0,6] (blank on one side, six dots on the other) is not present. All other dominoes including [0,0], [0,1], [0,2], [0,3], [0,4], [0,5] and all other combinations are accounted for in the image.