feat: add 8x8 DCT blockiness and social media compression heuristics

api/model_server.py

@@ -146,10 +146,45 @@ def check_photographic_domain(
             f"Non-photographic artwork."
         )
 
+    # 8x8 DCT JPEG Blockiness calculation
+    blockiness = 1.0
+    try:
+        import cv2
+        gray = cv2.cvtColor(np.array(img_rgb), cv2.COLOR_RGB2GRAY).astype(np.float32)
+        h_blocks = h // 8
+        if h_blocks > 2 and w > 16:
+            boundary_diff = np.mean([np.mean(np.abs(gray[i * 8, :] - gray[i * 8 - 1, :])) for i in range(1, h_blocks)])
+            interior_diff = np.mean([np.mean(np.abs(gray[i * 8 - 1, :] - gray[i * 8 - 2, :])) for i in range(1, h_blocks)])
+            blockiness = float(boundary_diff / (interior_diff + 1e-6))
+    except Exception:
+        blockiness = 1.0
+
+    # Social media compression indicators
+    social_media_keywords = [
+        "whatsapp", "telegram", "messenger", "instagram", "discord",
+        "facebook", "fb_", "signal", "wechat", "viber"
+    ]
+    has_sm_keyword = any(k in fname_lower for k in social_media_keywords)
+    is_social_media_compressed = has_sm_keyword or (blockiness > 1.25)
+
+    compression_warning = None
+    if is_social_media_compressed:
+        compression_warning = (
+            f"Social media lossy compression detected (8x8 DCT blockiness {blockiness:.2f}). "
+            f"Messaging platforms (WhatsApp/Telegram) discard high-frequency Fourier harmonics (see Manuscript Table 7). "
+            f"Treat 'Authentic' classifications with caution."
+        )
+
+    full_warning = warning
+    if compression_warning:
+        full_warning = f"{full_warning} | {compression_warning}" if full_warning else compression_warning
+
     return {
         "is_non_photographic_graphic": is_ood,
         "domain_status": domain_status,
-        "warning": warning,
+        "is_social_media_compressed": is_social_media_compressed,
+        "compression_blockiness": round(blockiness, 3),
+        "warning": full_warning,
     }
 
 
@@ -252,10 +287,12 @@ class TamperingModelServer:
 
         elapsed_ms = (time.time() - start) * 1000.0
 
-        # Pre-flight domain inspection (draw.io, screenshots, blank canvas, anime/art)
+        # Pre-flight domain inspection (draw.io, screenshots, blank canvas, anime/art, social media compression)
         ood_info = check_photographic_domain(image, filename=filename)
         domain_status = ood_info["domain_status"]
         is_non_photographic = ood_info["is_non_photographic_graphic"]
+        is_sm_compressed = ood_info.get("is_social_media_compressed", False)
+        blockiness = ood_info.get("compression_blockiness", 1.0)
         warning = ood_info["warning"]
 
         conf = round(probs[pred_idx].item(), 4)
@@ -274,5 +311,7 @@ class TamperingModelServer:
             "model_variant": self.variant,
             "is_non_photographic_graphic": is_non_photographic,
             "domain_status": domain_status,
+            "is_social_media_compressed": is_sm_compressed,
+            "compression_blockiness": blockiness,
             "warning": warning,
         }