Domino

By systematically checking the 28 unique tiles of a standard double-six set against the 27 tiles provided in the image, it is observed that the blank-blank (0, 0) tile is the only one missing.

By systematically checking all 28 possible dominoes in a standard double-six set, I can identify which tiles are present in the image. After accounting for all visible dominoes including [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], [4,5], [4,6], [5,5], [5,6], and [6,6], the domino [4,4] is the only one missing from the complete set of 28 unique tiles.

I counted the pip totals for each number across the shown tiles and found the digit 6 appears two fewer times than it should in a full double-six set, which indicates the double-six (6-6) tile is missing.

By counting the occurrences of the number 0 (blank half) in the image, I find exactly 7 appearances: [0,0] contributes 2, and [0,1], [0,2], [0,3], [0,4], [0,5] each contribute 1. In a full double-six set, the number 0 appears 8 times. Since 27 dominoes are present (one missing), and 0 appears 7 times, the missing domino must contain a 0. The dominoes [0,0] through [0,5] are all visible in the image, so the only missing possibility is [0,6].