A thumbnail label earns its space when it clarifies something the image or title leaves unresolved. Repeating the full title in tiny lettering usually makes both elements harder to use.
Identify the missing clue
Look at the image without text and ask what remains ambiguous. A photograph of a repaired object may need a short label identifying the problem that was fixed. If the image already communicates the point, extra wording may be unnecessary.
Draft short alternatives
Write several labels with different purposes: identify the object, describe the outcome, or name the comparison. Choose the one that is both accurate and useful beside the title. Avoid unexplained fragments that sound dramatic but say little.
Test the pair
Read the title and thumbnail together as a single promise. Remove duplicate wording where it adds no value, and check that the label remains legible at a small size. If it requires a sentence of explanation, move that detail into the title or description instead.