diff --git a/idup.py b/idup.py
new file mode 100644
index 0000000..5e78699
--- /dev/null
+++ b/idup.py
@@ -0,0 +1,136 @@
+#!/usr/bin/env python3
+# find duplicate images given a hamming distance threshold.
+# employs dhash to do the heavy lifting.
+# doesn't recurse into "./_duplicate/" so you can dump things there if you wish.
+# dependencies: pillow, dhash
+
+import sys, os, os.path, pickle
+from PIL import Image
+import dhash
+
+def lament(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+def result(diff, p1, p2): # TODO: rename
+    print("{}\t{}\t{}".format(diff, p1, p2))
+
+dbname = "idup.db"
+exts = ".jpeg .jpg .png".split()
+
+rootpath = "."
+ignore_dir = os.path.join(rootpath, "_duplicate")
+
+"""verbosity:
+    -1: only unrecoverable errors.
+    0: include failures.
+    1: include image opening/hashing.
+    2: the kitchen sink.
+"""
+verbosity = 1
+
+pname = sys.argv[0]
+if len(sys.argv) <= 1:
+    print("usage: {} {{threshold}}".format(pname))
+    print("    utilizes {} in the current working directory".format(dbname))
+    sys.exit(1)
+args = sys.argv[1:]
+
+threshold = int(args[0])
+
+paths = {} # path to hash mapping.
+
+if os.path.exists(dbname) and os.path.getsize(dbname) > 0:
+    with open(dbname, "rb") as f:
+        paths = pickle.load(f)
+        #lament("loaded", len(paths.keys()), "hashes")
+else:
+    if verbosity >= 0:
+        lament("warning: no database found. starting from scratch.")
+
+existing = dict((path, h) for path, h in paths.items() if os.path.exists(path))
+for path in paths.keys():
+    if path not in existing:
+        if verbosity >= 0:
+            lament("#d", path)
+
+paths = existing
+
+def compare_hash(h1, h2):
+    # hashes are in byte strings, so we have to convert them to integers.
+    i1 = int.from_bytes(h1, byteorder="big")
+    i2 = int.from_bytes(h2, byteorder="big")
+    # return the hamming distance.
+    return bin(i1 ^ i2).count('1')
+
+def run():
+    for dn, _, fns in os.walk(rootpath):
+        if dn == ignore_dir:
+            continue
+
+        for fn in fns:
+            name, ext = os.path.splitext(fn)
+            path = os.path.join(dn, fn)
+            if ext not in exts:
+                continue
+
+            if path in paths:
+                if verbosity >= 2:
+                    lament("#s", path)
+                continue
+
+            try:
+                image = Image.open(path)
+            except OSError:
+                if verbosity >= 0:
+                    lament("#f", path)
+            else:
+                try:
+                    row, col = dhash.dhash_row_col(image)
+                except OSError:
+                    if verbosity >= 0:
+                        lament("#f", path)
+                else:
+                    if verbosity >= 1:
+                        lament("#o", path)
+                    h = dhash.format_bytes(row, col)
+                    paths[path] = h
+                finally:
+                    image.close()
+
+    # first pass: exact hash matching.
+    hashes = dict((v, k) for k, v in paths.items())
+    for p1, h in paths.items():
+        p2 = hashes[h]
+        if p1 != p2:
+            result(-1, p1, p2)
+
+    # second pass: fuzzy hash matching.
+    if threshold <= 0:
+        return
+    seen = set()
+    for p1, h1 in paths.items():
+        if verbosity >= 2:
+            lament("#c", p1)
+        seen.add(p1)
+        for p2, h2 in paths.items():
+            if p2 in seen:
+                continue
+            if h1 == h2:
+                continue
+            diff = compare_hash(h1, h2)
+            if diff <= threshold:
+                result(diff, p1, p2)
+
+try:
+    run()
+except KeyboardInterrupt:
+    if verbosity >= 0:
+        lament("# interrupted")
+finally:
+    if os.path.exists(dbname):
+        backup = dbname+".bak"
+        if os.path.exists(backup):
+            os.remove(backup)
+        os.rename(dbname, dbname+".bak")
+    with open(dbname, "wb") as f:
+        pickle.dump(paths, f)