diff --git a/.gitignore b/.gitignore
index 9afdab2..938ac35 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,5 @@ tests/deps/
 *.log
 *.html
 times.txt
+*_diff.png
+*.echo
diff --git a/gallery/HydraBot.png b/gallery/HydraBot.png
index cb745bd..b364ace 100644
Binary files a/gallery/HydraBot.png and b/gallery/HydraBot.png differ
diff --git a/gallery/readme.md b/gallery/readme.md
index 62ca8e6..0f008ff 100644
--- a/gallery/readme.md
+++ b/gallery/readme.md
@@ -7,7 +7,7 @@ Arduino thermostat to control a beer fridge to use it as an environmental chambe
 
 ---
 ## HydraBot
-Current state of HydraRaptor after being modified for laser engarving.
+Current state of HydraRaptor after being modified for laser engraving.
 
 ![](HydraBot.png)
 
diff --git a/scripts/gallery.py b/scripts/gallery.py
index 4d08bfe..96faadb 100644
--- a/scripts/gallery.py
+++ b/scripts/gallery.py
@@ -28,6 +28,7 @@ from colorama import Fore, init
 from tests import do_cmd
 import re
 from shutil import copyfile
+from tests import update_image
 
 project_dir = '../..'
 target_dir = 'gallery'
@@ -53,7 +54,10 @@ def gallery():
                             if image.startswith('![Main Assembly](assemblies/'):
                                 file = image[17 : -1]
                                 line = line.replace(image, '![](%s.png)' % project)
-                                copyfile(path + '/' + file, '%s/%s.png' %(target_dir, project))
+                                tmp_name = 'tmp.png'
+                                target_name = '%s/%s.png' %(target_dir, project)
+                                copyfile(path + '/' + file, tmp_name)
+                                update_image(tmp_name, target_name)
                             else:
                                 line = line.replace(image, '')
                         else:
diff --git a/scripts/tests.py b/scripts/tests.py
index 754c4d0..63d34bd 100644
--- a/scripts/tests.py
+++ b/scripts/tests.py
@@ -28,8 +28,10 @@ import bom
 import times
 import time
 import json
+import shutil
 from deps import *
 from blurb import *
+from colorama import Fore
 
 w = 4096
 h = w
@@ -38,7 +40,20 @@ def do_cmd(cmd, output = sys.stdout):
     for arg in cmd:
         print(arg, end = " ")
     print()
-    subprocess.call(cmd, stdout = output)
+    return subprocess.call(cmd, stdout = output, stderr = output)
+
+def update_image(tmp_name, png_name):
+    """Update an image only if different, otherwise just change the mod time"""
+    with open(os.devnull, 'w') as null:
+        diff_name = png_name.replace('.png', '_diff.png')
+        if not os.path.isfile(png_name) or do_cmd(("magick compare -metric AE %s %s %s" % (png_name, tmp_name, diff_name)).split(), output = null):
+            shutil.copyfile(tmp_name, png_name)
+            print(Fore.GREEN + png_name + " updated" + Fore.WHITE)
+        else:
+            os.utime(png_name, None)
+            os.remove(diff_name)
+        os.remove(tmp_name)
+
 
 def depluralise(name):
     if name[-3:] == "ies" and name != "zipties":
@@ -159,9 +174,11 @@ def tests(tests):
             if changed:
                 print(changed)
                 t = time.time()
-                openscad.run("-D", "$bom=2", "--projection=p", "--imgsize=%d,%d" % (w, h), "--camera=0,0,0,70,0,315,500", "--autocenter", "--viewall", "-d", dname, "-o", png_name, scad_name);
+                tmp_name = 'tmp.png'
+                openscad.run("-D", "$bom=2", "--projection=p", "--imgsize=%d,%d" % (w, h), "--camera=0,0,0,70,0,315,500", "--autocenter", "--viewall", "-d", dname, "-o", tmp_name, scad_name);
                 times.add_time(scad_name, t)
-                do_cmd(["magick", png_name, "-trim", "-resize", "1000x600", "-bordercolor", "#ffffe5", "-border", "10", png_name])
+                do_cmd(["magick", tmp_name, "-trim", "-resize", "1000x600", "-bordercolor", "#ffffe5", "-border", "10", tmp_name])
+                update_image(tmp_name, png_name)
                 BOM = bom.parse_bom()
                 with open(bom_name, 'wt') as outfile:
                     json.dump(BOM.flat_data(), outfile, indent = 4)
diff --git a/scripts/views.py b/scripts/views.py
index 8bdb095..60d3a7d 100644
--- a/scripts/views.py
+++ b/scripts/views.py
@@ -25,7 +25,7 @@
 from __future__ import print_function
 from set_config import *
 import openscad
-from tests import do_cmd
+from tests import do_cmd, update_image
 import time
 import times
 from deps import *
@@ -33,6 +33,7 @@ import os
 import json
 import blurb
 import bom
+import shutil
 from colorama import Fore
 
 def is_assembly(s):
@@ -151,12 +152,15 @@ def views(target, do_assemblies = None):
                                         if changed:
                                             print(changed)
                                             t = time.time()
-                                            openscad.run("-D$pose=1", "-D$explode=%d" % explode, "--projection=p", "--imgsize=4096,4096", "--autocenter", "--viewall", "-d", dname, "-o", png_name, png_maker_name);
+                                            tmp_name = 'tmp.png'
+                                            openscad.run("-D$pose=1", "-D$explode=%d" % explode, "--projection=p", "--imgsize=4096,4096", "--autocenter", "--viewall", "-d", dname, "-o", tmp_name, png_maker_name);
                                             times.add_time(png_name, t)
-                                            do_cmd(["magick", png_name, "-trim", "-resize", "1004x1004", "-bordercolor", "#ffffe5", "-border", "10", png_name])
+                                            do_cmd(["magick", tmp_name, "-trim", "-resize", "1004x1004", "-bordercolor", "#ffffe5", "-border", "10", tmp_name])
+                                            update_image(tmp_name, png_name)
                                         tn_name = png_name.replace('.png', '_tn.png')
                                         if mtime(png_name) > mtime(tn_name):
-                                            do_cmd(("magick "+ png_name + " -trim -resize 280x280 -background #ffffe5 -gravity Center -extent 280x280 -bordercolor #ffffe5 -border 10 " + tn_name).split())
+                                            do_cmd(("magick "+ png_name + " -trim -resize 280x280 -background #ffffe5 -gravity Center -extent 280x280 -bordercolor #ffffe5 -border 10 " + tmp_name).split())
+                                            update_image(tmp_name, tn_name)
                                     os.remove(png_maker_name)
                                 done_assemblies.append(module)
                             else: