arXiv — NLP / Computation & Language · · 3 min read

Resolution Thresholds in VLM Detection of Harmful ASCII Art Across Construction Modes and Languages

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Computer Science > Computation and Language

arXiv:2606.29649 (cs)
[Submitted on 28 Jun 2026]

Title:Resolution Thresholds in VLM Detection of Harmful ASCII Art Across Construction Modes and Languages

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Abstract:Large Vision-Language Models (VLMs) are increasingly deployed as content moderation tools, yet they remain vulnerable to jailbreak attacks in which harmful text is visually encoded as ASCII art. This can allow inappropriate or harmful content to bypass moderation systems. To address this vulnerability, this paper investigates how image resolution affects VLM detection of harmful ASCII art across eight character construction modes (L1-L8), ranging from dense block characters to word-embedded designs. We evaluate eight state-of-the-art VLMs on English and Chinese corpora using a pipeline that generates ASCII art images at ten resolution scales, probing whether a consistent detection-failure threshold exists across models, modes, and languages. Results indicate that detection rates decline sharply above certain resolution thresholds, and that word-based modes are the most resistant to detection across the full resolution range. These findings reveal a systematic vulnerability in VLM-based content moderation systems and motivate resolution-aware evaluation standards.
Comments: 13 pages, 9 figures, 3 tables
Subjects: Computation and Language (cs.CL)
Cite as: arXiv:2606.29649 [cs.CL]
  (or arXiv:2606.29649v1 [cs.CL] for this version)
  https://doi.org/10.48550/arXiv.2606.29649
arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Yikai Hua [view email]
[v1] Sun, 28 Jun 2026 23:36:52 UTC (1,426 KB)
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