feat(metadata): detect China TC260 AIGC PNG chunk and HuggingFace hf-job-id

aigc_label now reads the TC260 label from a raw-JSON `AIGC` PNG tEXt chunk
(as Doubao/ByteDance write it, with no namespaced XMP marker) in addition to
the `<TC260:AIGC>` XMP block, via a shared _parse helper gated on a TC260 field
so a generic AIGC key cannot false-positive. New huggingface_job() reads the
hf-job-id PNG chunk; identify surfaces it as a medium-confidence hf_job signal
(parallel to the visible sparkle, never overriding a hard metadata verdict).
Both wired into has_ai_metadata/get_ai_metadata; the PNG save whitelist already
strips them on removal. Found by auditing 646 corpus originals: 28 AIGC and 3
hf-job files the library previously reported as Unknown.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_identify.py

@@ -201,6 +201,78 @@ class TestIdentifyLocalParams:
         assert r.signals == []
 
 
+# ── China TC260 AIGC label as a PNG text chunk (Doubao) ─────────────
+
+
+class TestIdentifyAigcPngChunk:
+    """The raw-JSON ``AIGC`` PNG chunk (no namespaced XMP marker) is a high-
+    confidence AI verdict, same as the XMP form."""
+
+    def _aigc_chunk_png(self, tmp_path: Path) -> Path:
+        from PIL import Image
+        from PIL.PngImagePlugin import PngInfo
+
+        p = tmp_path / "doubao_chunk.png"
+        pnginfo = PngInfo()
+        pnginfo.add_text("AIGC", json.dumps({"Label": "1", "ContentProducer": "doubao"}))
+        Image.new("RGB", (32, 32)).save(p, pnginfo=pnginfo)
+        return p
+
+    def test_png_chunk_detected_high(self, tmp_path: Path):
+        r = identify(self._aigc_chunk_png(tmp_path), check_visible=False)
+        assert r.is_ai_generated is True
+        assert r.confidence == "high"
+        assert r.platform is not None
+        assert "AIGC" in r.platform
+        signal = next(s for s in r.signals if s.name == "aigc")
+        assert "doubao" in signal.detail
+
+
+# ── HuggingFace-hosted job marker (medium confidence) ───────────────
+
+
+class TestIdentifyHuggingFaceJob:
+    """The hf-job-id chunk lifts an otherwise-Unknown verdict to a tentative
+    (medium) AI, never overriding a high-confidence metadata signal."""
+
+    def _hf_png(self, tmp_path: Path) -> Path:
+        from PIL import Image
+        from PIL.PngImagePlugin import PngInfo
+
+        p = tmp_path / "hfjob.png"
+        pnginfo = PngInfo()
+        pnginfo.add_text("hf-job-id", "ec8380a6-2091-423a-b835-209420f99ee1")
+        Image.new("RGB", (32, 32)).save(p, pnginfo=pnginfo)
+        return p
+
+    def test_hf_job_promotes_to_medium(self, tmp_path: Path):
+        r = identify(self._hf_png(tmp_path), check_visible=False)
+        assert r.is_ai_generated is True
+        assert r.confidence == "medium"
+        assert r.platform is not None
+        assert "HuggingFace" in r.platform
+        signal = next(s for s in r.signals if s.name == "hf_job")
+        assert signal.confidence == "medium"
+
+    def test_hf_job_caveat_present(self, tmp_path: Path):
+        r = identify(self._hf_png(tmp_path), check_visible=False)
+        assert any("hf-job-id" in c for c in r.caveats)
+
+    def test_metadata_keeps_high_even_with_hf_job(self, tmp_png_with_ai_metadata: Path):
+        # A high-confidence metadata verdict is not downgraded by an hf-job hit.
+        from PIL import Image
+        from PIL.PngImagePlugin import PngInfo
+
+        img = Image.open(tmp_png_with_ai_metadata)
+        pnginfo = PngInfo()
+        for k, v in img.text.items():
+            pnginfo.add_text(k, v)
+        pnginfo.add_text("hf-job-id", "ec8380a6-2091-423a-b835-209420f99ee1")
+        img.save(tmp_png_with_ai_metadata, pnginfo=pnginfo)
+        r = identify(tmp_png_with_ai_metadata, check_visible=False)
+        assert r.confidence == "high"
+
+
 # ── Visible-sparkle fallback (mocked detector) ──────────────────────
 
 

tests/test_metadata.py

@@ -554,6 +554,88 @@ class TestAIGCLabel:
         assert "aigc_label" in meta
         assert "TC260" in meta["aigc_label"]
 
+    def _aigc_chunk_png(self, tmp_path: Path, producer: str = "doubao") -> Path:
+        """Doubao writes the TC260 object as a PNG ``tEXt`` chunk keyed ``AIGC``
+        with raw JSON (no XMP, no namespaced marker)."""
+        import json
+
+        p = tmp_path / "doubao_chunk.png"
+        pnginfo = PngInfo()
+        pnginfo.add_text(
+            "AIGC",
+            json.dumps({"Label": "1", "ContentProducer": producer, "ProduceID": "abc123"}),
+        )
+        Image.new("RGB", (32, 32)).save(p, pnginfo=pnginfo)
+        return p
+
+    def test_parses_png_text_chunk_form(self, tmp_path: Path):
+        from remove_ai_watermarks.metadata import aigc_label
+
+        info = aigc_label(self._aigc_chunk_png(tmp_path))
+        assert info is not None
+        assert info["Label"] == "1"
+        assert info["ContentProducer"] == "doubao"
+
+    def test_png_chunk_without_tc260_field_ignored(self, tmp_path: Path):
+        """A generic ``AIGC`` chunk with no TC260 field must not false-positive."""
+        import json
+
+        from remove_ai_watermarks.metadata import aigc_label
+
+        p = tmp_path / "unrelated.png"
+        pnginfo = PngInfo()
+        pnginfo.add_text("AIGC", json.dumps({"unrelated": "value"}))
+        Image.new("RGB", (32, 32)).save(p, pnginfo=pnginfo)
+        assert aigc_label(p) is None
+
+    def test_has_ai_metadata_detects_png_chunk_form(self, tmp_path: Path):
+        assert has_ai_metadata(self._aigc_chunk_png(tmp_path))
+
+    def test_remove_strips_png_chunk_form(self, tmp_path: Path):
+        from remove_ai_watermarks.metadata import aigc_label, remove_ai_metadata
+
+        out = tmp_path / "clean.png"
+        remove_ai_metadata(self._aigc_chunk_png(tmp_path), out)
+        assert aigc_label(out) is None
+        assert not has_ai_metadata(out)
+
+
+class TestHuggingFaceJob:
+    """HuggingFace-hosted job marker (``hf-job-id`` PNG text chunk)."""
+
+    def _hf_png(self, tmp_path: Path, job_id: str = "ec8380a6-2091-423a-b835-209420f99ee1") -> Path:
+        p = tmp_path / "hfjob.png"
+        pnginfo = PngInfo()
+        pnginfo.add_text("hf-job-id", job_id)
+        Image.new("RGB", (32, 32)).save(p, pnginfo=pnginfo)
+        return p
+
+    def test_returns_job_id(self, tmp_path: Path):
+        from remove_ai_watermarks.metadata import huggingface_job
+
+        assert huggingface_job(self._hf_png(tmp_path)) == "ec8380a6-2091-423a-b835-209420f99ee1"
+
+    def test_none_when_absent(self, tmp_clean_png):
+        from remove_ai_watermarks.metadata import huggingface_job
+
+        assert huggingface_job(tmp_clean_png) is None
+
+    def test_has_ai_metadata_detects_hf_job(self, tmp_path: Path):
+        assert has_ai_metadata(self._hf_png(tmp_path))
+
+    def test_get_ai_metadata_surfaces_hf_job(self, tmp_path: Path):
+        meta = get_ai_metadata(self._hf_png(tmp_path))
+        assert "huggingface_job" in meta
+        assert "ec8380a6" in meta["huggingface_job"]
+
+    def test_remove_strips_hf_job(self, tmp_path: Path):
+        from remove_ai_watermarks.metadata import huggingface_job, remove_ai_metadata
+
+        out = tmp_path / "clean.png"
+        remove_ai_metadata(self._hf_png(tmp_path), out)
+        assert huggingface_job(out) is None
+        assert not has_ai_metadata(out)
+
 
 @pytest.mark.skipif(not (SAMPLES_DIR / "doubao-1.png").exists(), reason="doubao sample not present")
 class TestAIGCRealSample: