diff --git a/app/models/slideshow_block.rb b/app/models/slideshow_block.rb
index a34adbb..e47aa73 100644
--- a/app/models/slideshow_block.rb
+++ b/app/models/slideshow_block.rb
@@ -4,6 +4,7 @@ class SlideshowBlock < Block
   settings_items :interval, :type => 'integer', :default => 4
   settings_items :shuffle, :type => 'boolean', :default => false
   settings_items :navigation, :type => 'boolean', :default => false
+  settings_items :image_size, :type => 'string', :default => 'thumb'
 
   def self.description
     _('Slideshow')
@@ -13,6 +14,19 @@ class SlideshowBlock < Block
     gallery_id ? Folder.find(:first, :conditions => { :id => gallery_id }) : nil
   end
 
+  def public_filename_for(image)
+    check_filename(image, image_size) || check_filename(image, 'thumb')
+  end
+
+  def check_filename(image, size)
+    filename = image.public_filename(size)
+    if File.exists?(File.join(Rails.root, 'public', filename))
+      filename
+    else
+      nil
+    end
+  end
+
   def block_images
     gallery.images.reject {|item| item.folder?}
   end
diff --git a/app/models/uploaded_file.rb b/app/models/uploaded_file.rb
index 2fa561c..8918583 100644
--- a/app/models/uploaded_file.rb
+++ b/app/models/uploaded_file.rb
@@ -21,7 +21,7 @@ class UploadedFile < Article
   #  :min_size => 2.megabytes
   #  :max_size => 5.megabytes
   has_attachment :storage => :file_system,
-    :thumbnails => { :icon => [24,24], :thumb => '130x130>', :display => '640X480>' },
+    :thumbnails => { :icon => [24,24], :thumb => '130x130>', :slideshow => '320x240>', :display => '640X480>' },
     :thumbnail_class => Thumbnail,
     :max_size => 5.megabytes # remember to update validate message below
 
diff --git a/app/views/blocks/slideshow.rhtml b/app/views/blocks/slideshow.rhtml
index 48c0a3b..a06396a 100644
--- a/app/views/blocks/slideshow.rhtml
+++ b/app/views/blocks/slideshow.rhtml
@@ -5,7 +5,7 @@
     <div class='slideshow-container'>
       <% images.each do |img| %>
         <a href="<%= url_for(img.external_link.blank? ? img.view_url: img.external_link) %>">
-          <%= content_tag('div', '', :style => "background-image: url(#{img.public_filename(:thumb)})", :title => (img.abstract.blank? ? '' : img.abstract)) %>
+          <%= content_tag('div', '', :style => "background-image: url(#{block.public_filename_for(img)})", :title => (img.abstract.blank? ? '' : img.abstract)) %>
           <% if !img.abstract.blank? %>
             <span class='image-description'><%= img.abstract %></span>
           <% end %>
diff --git a/app/views/box_organizer/_slideshow_block.rhtml b/app/views/box_organizer/_slideshow_block.rhtml
index 2d1b293..b13d555 100644
--- a/app/views/box_organizer/_slideshow_block.rhtml
+++ b/app/views/box_organizer/_slideshow_block.rhtml
@@ -3,6 +3,8 @@
   [ _('%{gallery} (%{count} images)') % {:gallery => item.path, :count => item.images.reject{|image| image.folder?}.count}, item.id ]
 }) %>
 
+<%= labelled_form_field(_('Image size'), select('block', 'image_size', [[_('Miniatura'), 'thumb'],[_('Slideshow size'), 'slideshow']])) %>
+
 <%= labelled_form_field _('Image transition:'), select('block', 'interval', [[_('No automatic transition'), 0]] + [1, 2, 3, 4, 5, 10, 20, 30, 60].map {|item| [n_('Every 1 second', 'Every %d seconds', item) % item, item]}) %>
 
 <%= labelled_form_field check_box(:block, :shuffle) + _('Show images in random order'), '' %>
diff --git a/test/unit/slideshow_block_test.rb b/test/unit/slideshow_block_test.rb
index 32367bf..a274592 100644
--- a/test/unit/slideshow_block_test.rb
+++ b/test/unit/slideshow_block_test.rb
@@ -65,4 +65,36 @@ class SlideshowBlockTest < ActiveSupport::TestCase
     assert_not_includes block.block_images, folder
   end
 
+  should 'display "thumb" size by default' do
+    assert_equal 'thumb', SlideshowBlock.new.image_size
+  end
+
+  should 'set different image size' do
+    block = SlideshowBlock.new(:image_size => 'slideshow')
+    assert_equal 'slideshow', block.image_size
+  end
+
+  should 'decide correct public filename for image' do
+    image = mock
+    image.expects(:public_filename).with('slideshow').returns('/bli/slideshow.png')
+    File.expects(:exists?).with("#{Rails.root}/public/bli/slideshow.png").returns(true)
+
+    assert_equal '/bli/slideshow.png', SlideshowBlock.new(:image_size => 'slideshow').public_filename_for(image)
+  end
+
+  should 'fallback to existing size in case the requested size does not exist' do
+    block = SlideshowBlock.new(:image_size => 'slideshow')
+
+    image = mock
+    # "slideshow" size does not exist
+    image.expects(:public_filename).with('slideshow').returns('/bli/slideshow.png')
+    File.expects(:exists?).with("#{Rails.root}/public/bli/slideshow.png").returns(false) # <<<<<
+
+    # thumb size does exist
+    image.expects(:public_filename).with('thumb').returns('/bli/thumb.png')
+    File.expects(:exists?).with("#{Rails.root}/public/bli/thumb.png").returns(true) # <<<<<
+
+    assert_equal '/bli/thumb.png', block.public_filename_for(image)
+  end
+
 end
--
libgit2 0.21.2