diff --git a/presentation_validator/unique_ids.py b/presentation_validator/unique_ids.py
new file mode 100644
index 0000000..c08f486
--- /dev/null
+++ b/presentation_validator/unique_ids.py
@@ -0,0 +1,79 @@
+import sys
+import json
+from typing import List, Set, Tuple
+from presentation_validator.model import ErrorDetail
+from presentation_validator.v3.schemavalidator import create_snippet
+
+IGNORE: Set[str] = {
+    "target",
+    "lookAt",
+    "range",
+    "structures",
+    "first",
+    "last",
+    "start",
+    "source",
+    "body",
+    "scope",
+    "thumbnail",
+}
+MAX_DEPTH: int = 1000
+
+
+class MaxDepthExceeded(Exception):
+    pass
+
+
+def check(manifest) -> List[ErrorDetail]:
+    """
+    Checks that all values associated with the key 'id' are globally unique.
+
+    Args:
+        manifest: the root JSON dict
+
+    Returns:
+        A generator of ErrorDetail objects for each duplicate ID found.
+        The generator is empty if no duplicates are found.
+
+    Raises:
+        MaxDepthExceeded: If MAX_DEPTH is exceeded in the search.
+    """
+    seen_ids = []
+    # stores tuples of (search depth, path, node)
+    stack: List[Tuple[int, str, dict]] = [(0, "", manifest)]
+    while stack:
+        depth, path, node = stack.pop()
+        if depth > MAX_DEPTH:
+            raise MaxDepthExceeded(f"Max search depth {MAX_DEPTH} exceeded at {node}")
+        for key, value in filter(lambda x: x[0] not in IGNORE, node.items()):
+            if key == "id" or key == "@id":
+                if value in seen_ids:
+                    yield ErrorDetail(
+                        f"Duplicate id found",
+                        "The id field must be unique",
+                        f"Duplicate id: {value}",
+                        path + "/" + key,
+                        create_snippet(node),
+                        None,
+                    )
+                seen_ids.append(value)
+            elif isinstance(value, list):
+                for i, item in enumerate(value):
+                    # only dicts can contain IDs
+                    if isinstance(item, dict):
+                        stack.append((depth + 1, f"{path}/{key}[{i}]", item))
+
+
+def main():
+    # pass in manifest by command line argument
+    # load json from file
+    with open(sys.argv[1], "r") as f:
+        manifest = json.load(f)
+
+    errors = check(manifest)
+    for err in errors:
+        print(err)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/presentation_validator/v4/unique_ids.py b/presentation_validator/v4/unique_ids.py
deleted file mode 100644
index 7126769..0000000
--- a/presentation_validator/v4/unique_ids.py
+++ /dev/null
@@ -1,61 +0,0 @@
-import sys
-import json
-from presentation_validator.model import ErrorDetail
-from presentation_validator.v3.schemavalidator import create_snippet
-
-ignore = ["target", "lookAt", "range","structures","first","last","start","source","body","scope"]
-# create a method where you pass in a manifest and it checks to see if the id is unique
-# if it is not unique, then it should raise a validation error  
-def check(manifest):
-
-    duplicates = []
-    ids = []
-    checkNode(manifest, ids, duplicates) 
-
-    if len(duplicates) > 0:
-        return duplicates
-    else:
-        return None    
-
-def checkNode(node, ids=[], duplicates=[], path = ""):
-    if type(node) != dict:
-        return 
-
-    for key, value in node.items():
-        if key == 'id':
-            if type(value) != str:
-                raise ValueError(f"Id must be a string: {value}")
-            if value in ids:
-                duplicates.append(ErrorDetail(
-                    f"Duplicate id found",
-                    "The id field must be unique",
-                    f"Duplicate id: {value}",
-                    path + "/" + key,
-                    create_snippet(node),
-                    None
-                ))
-            ids.append(value)
-        else:
-            # Don't look further in fields that point to other resources
-            if key in ignore:
-                continue
-
-            if type(value) == list:
-                count = 0
-                for item in value:
-                    checkNode(item, ids, duplicates, path + "/" + key + "[" + str(count) + "]")
-                    count += 1
-
-            elif type(value) != str:
-                checkNode(value, ids, duplicates, path + "/" + key)    
-
-def main():
-    # pass in manifest by command line argument
-    # load json from file
-    with open(sys.argv[1], 'r') as f:
-        manifest = json.load(f)
-
-    check(manifest)                
-
-if __name__ == '__main__':
-    main()
\ No newline at end of file
diff --git a/presentation_validator/v4/validation4.py b/presentation_validator/v4/validation4.py
index 9426895..5910f64 100644
--- a/presentation_validator/v4/validation4.py
+++ b/presentation_validator/v4/validation4.py
@@ -4,7 +4,6 @@
 import sys
 from presentation_validator.model import ValidationResult
 from presentation_validator.v3.schemavalidator import convertValidationError
-from presentation_validator.v4.unique_ids import check
 
 from jsonschema import Draft202012Validator
 from jsonschema.exceptions import relevance
@@ -51,18 +50,11 @@ def validate(instance):
         # Now create some useful messsages to pass on
         for err in errors:
             result.errorList.append(convertValidationError(err, errorCount, len(errors)))
-            
+
             errorCount += 1
     else:
         result.passed = True
 
-    duplicate_ids = check(instance)
-    if duplicate_ids:
-        result.passed = False
-
-        # Add all of the examples of duplicated ids
-        result.errorList.extend(duplicate_ids)
-    
     return result
 
 def main():
diff --git a/presentation_validator/validator.py b/presentation_validator/validator.py
index 62d456c..3ebb888 100644
--- a/presentation_validator/validator.py
+++ b/presentation_validator/validator.py
@@ -4,6 +4,7 @@
 from presentation_validator.v3 import schemavalidator
 from presentation_validator.v4 import validation4
 from presentation_validator.enum import IIIFVersion
+from presentation_validator import unique_ids
 
 import requests
 from urllib.parse import urlparse
@@ -102,6 +103,9 @@ def check_manifest(
         result.error = str(err)
         result.url = url
 
+    # Check for duplicate ID's in the manifest
+    result.errorList.extend(unique_ids.check(manifest))
+
     return result
 
 def fetch_manifest(url, accept, version):