@inproceedings{he-etal-2026-latent,
title = "Latent Visual Sensitive Fingerprinting for Black-Box Vision{--}Language Model Tamper Detection",
author = "He, Chaoxiang and
Chai, Jichen and
Hu, Hanqing and
Wang, Yi and
Wang, Shuo and
Hu, Hongsheng and
Zhu, Bin Benjamin",
editor = "Lee, Hung-Yi and
Dev, Sunipa and
Li, Jessy and
Elliott, Desmond",
booktitle = "Findings of the {A}ssociation for {C}omputational {L}inguistics: {EMNLP} 2026",
month = oct,
year = "2026",
address = "Budapest, Hungary",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2026.findings-emnlp.2178/",
pages = "46570--46589",
ISBN = "979-8-89176-462-0",
abstract = "Cloud-hosted vision-language models (VLMs) may be silently fine-tuned, poisoned, compressed, or replaced after deployment, motivating black-box fingerprint verification. RESF tests response distributions but requires estimating the service temperature, making its reliability sensitive to estimation error. We propose \textit{Latent Visual Sensitive Fingerprinting ($\mathtt{LVSF}$)}, based on a local Pearson-sensitivity decomposition of the conditional top-$k$ distribution of the first generated token. This decomposition separates observable output shifts from input-dependent exposure to parameter changes. Modeling tampering-induced relative top-$k$ logit shifts as isotropic, we show that a uniform top-$k$ anchor maximizes average sensitivity. Accordingly, $\mathtt{LVSF}$ equalizes recorded top-$k$ logits, maintains a margin from out-of-support tokens, and maximizes full-parameter Fisher sensitivity, yielding a reference distribution invariant to positive temperature scaling. These principles apply to both LLMs and VLMs. For VLMs, $\mathtt{LVSF}$ fixes a natural-language query and optimizes an image in a pretrained VAE latent space to produce natural-looking fingerprints. Repeated API queries detect excess out-of-support first tokens or shifts in conditional in-support frequencies. Across four VLMs and multiple tampering types, $\mathtt{LVSF}$ achieves consistently high detection rates with no observed false positives and substantially higher detection rates than evaluated baselines on Qwen2.5-VL-7B-Instruct."
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<abstract>Cloud-hosted vision-language models (VLMs) may be silently fine-tuned, poisoned, compressed, or replaced after deployment, motivating black-box fingerprint verification. RESF tests response distributions but requires estimating the service temperature, making its reliability sensitive to estimation error. We propose Latent Visual Sensitive Fingerprinting (\mathttLVSF), based on a local Pearson-sensitivity decomposition of the conditional top-k distribution of the first generated token. This decomposition separates observable output shifts from input-dependent exposure to parameter changes. Modeling tampering-induced relative top-k logit shifts as isotropic, we show that a uniform top-k anchor maximizes average sensitivity. Accordingly, \mathttLVSF equalizes recorded top-k logits, maintains a margin from out-of-support tokens, and maximizes full-parameter Fisher sensitivity, yielding a reference distribution invariant to positive temperature scaling. These principles apply to both LLMs and VLMs. For VLMs, \mathttLVSF fixes a natural-language query and optimizes an image in a pretrained VAE latent space to produce natural-looking fingerprints. Repeated API queries detect excess out-of-support first tokens or shifts in conditional in-support frequencies. Across four VLMs and multiple tampering types, \mathttLVSF achieves consistently high detection rates with no observed false positives and substantially higher detection rates than evaluated baselines on Qwen2.5-VL-7B-Instruct.</abstract>
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%0 Conference Proceedings
%T Latent Visual Sensitive Fingerprinting for Black-Box Vision–Language Model Tamper Detection
%A He, Chaoxiang
%A Chai, Jichen
%A Hu, Hanqing
%A Wang, Yi
%A Wang, Shuo
%A Hu, Hongsheng
%A Zhu, Bin Benjamin
%Y Lee, Hung-Yi
%Y Dev, Sunipa
%Y Li, Jessy
%Y Elliott, Desmond
%S Findings of the Association for Computational Linguistics: EMNLP 2026
%D 2026
%8 October
%I Association for Computational Linguistics
%C Budapest, Hungary
%@ 979-8-89176-462-0
%F he-etal-2026-latent
%X Cloud-hosted vision-language models (VLMs) may be silently fine-tuned, poisoned, compressed, or replaced after deployment, motivating black-box fingerprint verification. RESF tests response distributions but requires estimating the service temperature, making its reliability sensitive to estimation error. We propose Latent Visual Sensitive Fingerprinting (\mathttLVSF), based on a local Pearson-sensitivity decomposition of the conditional top-k distribution of the first generated token. This decomposition separates observable output shifts from input-dependent exposure to parameter changes. Modeling tampering-induced relative top-k logit shifts as isotropic, we show that a uniform top-k anchor maximizes average sensitivity. Accordingly, \mathttLVSF equalizes recorded top-k logits, maintains a margin from out-of-support tokens, and maximizes full-parameter Fisher sensitivity, yielding a reference distribution invariant to positive temperature scaling. These principles apply to both LLMs and VLMs. For VLMs, \mathttLVSF fixes a natural-language query and optimizes an image in a pretrained VAE latent space to produce natural-looking fingerprints. Repeated API queries detect excess out-of-support first tokens or shifts in conditional in-support frequencies. Across four VLMs and multiple tampering types, \mathttLVSF achieves consistently high detection rates with no observed false positives and substantially higher detection rates than evaluated baselines on Qwen2.5-VL-7B-Instruct.
%U https://aclanthology.org/2026.findings-emnlp.2178/
%P 46570-46589
Markdown (Informal)
[Latent Visual Sensitive Fingerprinting for Black-Box Vision–Language Model Tamper Detection](https://aclanthology.org/2026.findings-emnlp.2178/) (He et al., Findings 2026)
ACL