Feature (frontend): Add invisible watermark decoder node. (#8967)

* Initial plan

* Add invisible watermark decoding node and utility method

Co-authored-by: lstein <111189+lstein@users.noreply.github.com>

* chore(frontend): typegen

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: lstein <111189+lstein@users.noreply.github.com>

invokeai/app/invocations/image.py

@@ -21,7 +21,7 @@ from invokeai.app.invocations.fields import (
     WithBoard,
     WithMetadata,
 )
-from invokeai.app.invocations.primitives import ImageOutput
+from invokeai.app.invocations.primitives import ImageOutput, StringOutput
 from invokeai.app.services.image_records.image_records_common import ImageCategory
 from invokeai.app.services.shared.invocation_context import InvocationContext
 from invokeai.app.util.misc import SEED_MAX
@@ -581,6 +581,25 @@ class ImageWatermarkInvocation(BaseInvocation, WithMetadata, WithBoard):
         return ImageOutput.build(image_dto)
 
 
+@invocation(
+    "decode_watermark",
+    title="Decode Invisible Watermark",
+    tags=["image", "watermark"],
+    category="image",
+    version="1.0.0",
+)
+class DecodeInvisibleWatermarkInvocation(BaseInvocation):
+    """Decode an invisible watermark from an image."""
+
+    image: ImageField = InputField(description="The image to decode the watermark from")
+    length: int = InputField(default=8, description="The expected watermark length in bytes")
+
+    def invoke(self, context: InvocationContext) -> StringOutput:
+        image = context.images.get_pil(self.image.image_name)
+        watermark = InvisibleWatermark.decode_watermark(image, self.length)
+        return StringOutput(value=watermark)
+
+
 @invocation(
     "mask_edge",
     title="Mask Edge",

invokeai/backend/image_util/invisible_watermark.py

@@ -9,7 +9,7 @@ import numpy as np
 from PIL import Image
 
 import invokeai.backend.util.logging as logger
-from invokeai.backend.image_util.imwatermark.vendor import WatermarkEncoder
+from invokeai.backend.image_util.imwatermark.vendor import WatermarkDecoder, WatermarkEncoder
 
 
 class InvisibleWatermark:
@@ -25,3 +25,25 @@ class InvisibleWatermark:
         encoder.set_watermark("bytes", watermark_text.encode("utf-8"))
         bgr_encoded = encoder.encode(bgr, "dwtDct")
         return Image.fromarray(cv2.cvtColor(bgr_encoded, cv2.COLOR_BGR2RGB)).convert("RGBA")
+
+    @classmethod
+    def decode_watermark(cls, image: Image.Image, length: int = 8) -> str:
+        """Attempt to decode an invisible watermark from an image.
+
+        Args:
+            image: The PIL Image to decode the watermark from.
+            length: The expected watermark length in bytes. Must match the length used when encoding.
+                The WatermarkDecoder requires the length in bits; this value is multiplied by 8 internally.
+
+        Returns:
+            The decoded watermark text, or an empty string if no watermark is detected or decoding fails.
+        """
+        logger.debug("Attempting to decode invisible watermark")
+        try:
+            bgr = cv2.cvtColor(np.array(image.convert("RGB")), cv2.COLOR_RGB2BGR)
+            decoder = WatermarkDecoder("bytes", length * 8)
+            watermark_bytes = decoder.decode(bgr, "dwtDct")
+            return watermark_bytes.decode("utf-8", errors="ignore").rstrip("\x00")
+        except Exception:
+            logger.debug("Failed to decode invisible watermark")
+            return ""