Image search in the BIOP

The algorithm divides the image into zones, measures contrasts, dominant colours and outlines, then calculates a compact signature. This signature is compared with those of the records; the resemblance is expressed as a percentage.

The image sent is not kept by default: only its fingerprint is used for the comparison, then deleted. The user may choose to save it in their search record.

Photograph the work from the front, flat, in even light, without glare. Frame the whole work against a neutral background. For a sculpture, take several angles: front, side, back. For an object, add a characteristic detail: signature, mark, break.

JPEG, PNG and HEIC formats are accepted, up to twenty megabytes. A high-definition photograph improves reliability, but the system tolerates imperfect images, such as a screenshot of a listing or a photo taken at an angle.

Results are ranked by similarity score. Above eighty per cent, the resemblance is strong and calls for immediate verification. Between sixty and eighty, the record may correspond to a neighbouring work by the same artist or workshop.

Below sixty, the results are informative. In every case, compare the details: dimensions, signature, restorations, condition. If you are unsure, contact the BIOP unit, attaching the photographs.

The visual fingerprint is an aid: a BIOP unit analyst examines any strong match before a conclusion is drawn. Possible errors — false match, false negative — are documented and monitored monthly.

Users are encouraged to report discrepancies, in order to improve the algorithm. The database's supervisory committee examines each year the quality of results and the fairness of treatment.