The Early Bird Identifies the Worm: You Can't Beat a Head Start in Long-Term Body Re-ID (ECHO-BID)

Person identification in unconstrained viewing environments presents significant challenges due to variations in distance, viewpoint, imaging conditions, and clothing. We introduce $\textbf{E}$va $\textbf{C}$lothes-Change from $\textbf{H}$idden $\textbf{O}$bjects - $\textbf{B}$ody $\textbf{ID}$entification (ECHO-BID), a class of long-term re-id models built on object-pretrained EVA-02 Large backbones. We compare ECHO-BID to 9 other models that vary systematically in backbone architecture, model size, scale of object classification pretraining, and transfer learning protocol. Models were evaluated on benchmark datasets across constrained, unconstrained, and occluded settings. ECHO-BID, with transfer learning on the most challenging clothes-change data, achieved state-of-the-art results on long-term re-id -- substantially outperforming other methods. ECHO-BID also surpassed other methods by a wide margin in occluded viewing scenarios. A combination of increased model size and Masked Image Modeling during pretraining underlie ECHO-BID's strong performance on long-term re-id. Notably, a smaller, but more challenging transfer learning dataset, generalized better across datasets than a larger, less challenging one. However, the larger dataset with an additional fine-tuning step proved best on the most difficult data. Selecting the correct pretrained backbone architecture and transfer learning protocols can drive substantial gains in long-term re-id performance.

Recognizing People by Body Shape Using Deep Networks of Images and Words

Common and important applications of person identification occur at distances and viewpoints in which the face is not visible or is not sufficiently resolved to be useful. We examine body shape as a biometric across distance and viewpoint variation. We propose an approach that combines standard object classification networks with representations based on linguistic (word-based) descriptions of bodies. Algorithms with and without linguistic training were compared on their ability to identify people from body shape in images captured across a large range of distances/views (close-range, 100m, 200m, 270m, 300m, 370m, 400m, 490m, 500m, 600m, and at elevated pitch in images taken by an unmanned aerial vehicle [UAV]). Accuracy, as measured by identity-match ranking and false accept errors in an open-set test, was surprisingly good. For identity-ranking, linguistic models were more accurate for close-range images, whereas non-linguistic models fared better at intermediary distances. Fusion of the linguistic and non-linguistic embeddings improved performance at all, but the farthest distance. Although the non-linguistic model yielded fewer false accepts at all distances, fusion of the linguistic and non-linguistic models decreased false accepts for all, but the UAV images. We conclude that linguistic and non-linguistic representations of body shape can offer complementary identity information for bodies that can improve identification in applications of interest.