In addition to these other answers, a commonly used metric in the literature is the k-Recall@R, or the portion of the top k ground-truth vectors that are found

In addition to these other answers, a commonly used metric in the literature is the k-Recall@R, or the portion of the top k ground-truth vectors that are found in the top R ANN queries. This parametrization can make it clearer when comparing between different approaches For your case, you might find it helpful to look at the excellent ann-benchmarks.com, and in particular the benchmarks for GIST, which is an image embedding.