diff --git a/lib/screenshot.rb b/lib/screenshot.rb
index bde61ec..f3ec439 100644
--- a/lib/screenshot.rb
+++ b/lib/screenshot.rb
@@ -5,7 +5,7 @@ require 'mini_magick'
 
 class Screenshot
   include Capybara::DSL
-  attr_accessor :theme, :theme_name
+  attr_accessor :theme
 
   def self.prepare
     Capybara.register_driver :poltergeist do |app|
@@ -19,30 +19,42 @@ class Screenshot
     end
   end
 
-  def initialize(theme_name)
-    @theme_name = theme_name
-    @theme = theme_name.parameterize.underscore
+  def initialize(theme)
+    @theme = OpenStruct.new(theme.merge(
+      slug: theme[:name].parameterize.underscore,
+      digest: Digest::MD5.new.hexdigest(theme[:colors])
+    ))
   end
 
   def generate_theme_image
-    puts "Generating image for theme #{theme_name}"
+    if File.exist? target_file
+      puts "Image for theme #{theme.name} already exists"
+      return
+    end
+
+    puts "Generating image for theme #{theme.name}"
     visit '/'
-    within ".theme_#{theme}" do
+    within ".theme_#{theme.slug}" do
       choose 'sidebar_theme_rd'
     end
     sleep 1
-    file = Tempfile.new([theme, ".png"])
+
+    file = Tempfile.new([theme.slug, ".png"])
     begin
       page.save_screenshot(file.path, full: true)
 
       MiniMagick::Tool::Convert.new do |convert|
         convert << file.path
         convert.crop '220x220+0+0'
-        convert << "source/images/theme/#{theme}.png"
+        convert << target_file
       end
     ensure
       file.close
       file.unlink
     end
   end
+
+  def target_file
+    "source/images/theme/#{theme.slug}-#{theme.digest}.png"
+  end
 end
\ No newline at end of file
diff --git a/lib/screenshot_generator.rb b/lib/screenshot_generator.rb
index cb64691..5d17356 100644
--- a/lib/screenshot_generator.rb
+++ b/lib/screenshot_generator.rb
@@ -9,7 +9,7 @@ class ScreenshotGenerator < ::Middleman::Extension
       Screenshot.prepare
       data = YAML.load_file('data/themes.yml')
       data.each do |theme|
-        Screenshot.new(theme[:name]).generate_theme_image
+        Screenshot.new(theme).generate_theme_image
       end
       puts "Hello World"
       # builder.run './my_deploy_script.sh'
diff --git a/source/images/theme/aubergine.png b/source/images/theme/aubergine-78c77bed831d7972c590f9bd03e152d8.png
similarity index 99%
rename from source/images/theme/aubergine.png
rename to source/images/theme/aubergine-78c77bed831d7972c590f9bd03e152d8.png
index 64cca93..fd98984 100644
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diff --git a/source/images/theme/base16_eighties_dark.png b/source/images/theme/base16_eighties_dark-75cab375f85855ef921fb80f9a061782.png
similarity index 99%
rename from source/images/theme/base16_eighties_dark.png
rename to source/images/theme/base16_eighties_dark-75cab375f85855ef921fb80f9a061782.png
index 2fda5dc..ac5935d 100644
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similarity index 99%
rename from source/images/theme/base16_eighties_light.png
rename to source/images/theme/base16_eighties_light-a46cf66777c2c54503e63b00d9082f43.png
index 4da1528..f7d1339 100644
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similarity index 99%
rename from source/images/theme/base16_tomorrow_night.png
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index f8128b1..8b6378b 100644
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diff --git a/source/images/theme/choco_mint.png b/source/images/theme/choco_mint-2fddb05d1683177eb4fb68ee4120e5e7.png
similarity index 99%
rename from source/images/theme/choco_mint.png
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diff --git a/source/images/theme/citrus.png b/source/images/theme/citrus-aabf89160991190ec0315e2a39ea76fa.png
similarity index 99%
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diff --git a/source/images/theme/digitalocean.png b/source/images/theme/digitalocean-e2d1eca6db4cc8a78abcfce1ebf50f5e.png
similarity index 99%
rename from source/images/theme/digitalocean.png
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diff --git a/source/images/theme/hoth.png b/source/images/theme/hoth-974a7d725a04044a85c116f730e221b0.png
similarity index 99%
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similarity index 99%
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similarity index 99%
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diff --git a/source/images/theme/monument.png b/source/images/theme/monument-7c8301d46a6d99fd5136c0ecbd55f631.png
similarity index 99%
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similarity index 99%
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diff --git a/source/images/theme/wegman.png b/source/images/theme/wegman-9fa5565d625a1e75be23738d64e056c2.png
similarity index 99%
rename from source/images/theme/wegman.png
rename to source/images/theme/wegman-9fa5565d625a1e75be23738d64e056c2.png
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diff --git a/source/images/theme/work_hard.png b/source/images/theme/work_hard-c12b3ea651f9389a50450ce93c2dba97.png
similarity index 99%
rename from source/images/theme/work_hard.png
rename to source/images/theme/work_hard-c12b3ea651f9389a50450ce93c2dba97.png
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diff --git a/source/index.html.erb b/source/index.html.erb
index 1856c0b..cded4ae 100644
--- a/source/index.html.erb
+++ b/source/index.html.erb
@@ -4,8 +4,9 @@ title: Slack Themes
 
 <% data.themes.each do |theme| %>
 <% theme_slug = theme[:name].parameterize.underscore %>
+<% digest = Digest::MD5.new.hexdigest(theme[:colors]) %>
 <label class="radio theme_label theme_<%= theme[:name].parameterize.underscore %>">
-    <img src="/images/theme/<%= theme_slug %>.png" class="theme_thumb"><br>
+    <img src="/images/theme/<%= theme_slug %>-<%= digest %>.png" class="theme_thumb"><br>
     <input name="sidebar_theme_rd" type="radio" value="<%= theme[:colors] %>" ng-model="theme" ng-change="setTheme()"> <%= theme[:name] %>
 </label>
 <% end %>