_form.html.erb

<%= photo_upload_box(@article, :picture) %>

_photo_upload_box.html.erb

<% javascript_tag do %>
$(document).ready(function() {
  $(function() {
    button = $("#button_upload_box");
    frame = $("#frame_upload_box");
    
  <% if object.new_record? %>
      action = '<%= url_for(:controller => 'temp_uploads', :action => 'create') %>';
      
      new AjaxUpload(button.attr('id'), {action: action,
        name: 'upload',
        responseType: 'json',
        autoSubmit: true,
        onSubmit: function(file, extension){
          if (! (extension && /^(jpg|png|jpeg|gif)$/.test(extension))){
              alert("<%= t("upload_box.invalid_extension") %>: ." + extension);
              return false; //cancel upload
          }
          button.val("<%= t("upload_box.loading") %>...");
          this.setData({'authenticity_token'  : '<%= form_authenticity_token if protect_against_forgery? %>'});
          this.disable(); },
        onComplete: function(file, response) {
          if(response['response'] == 'success'){
            $("#<%="#{klass_id}_#{field}"%>").val(response['filename']);
            image = frame.find("img");
            image.attr('src', response['thumb']);
          }else if(response['response'] == 'failure'){
            alert(response['message']);
          }else{
            alert("<%= t("upload_box.error") %>");
          }
          button.val("<%= t("upload_box.edit") %>");
          this.enable()}
      });
  <% else %>
    action = '<%= url_for(object) %>';
    
    new AjaxUpload(button.attr('id'), {action: action,
      name: '<%= "#{klass_id}[#{field}]" %>',
      autoSubmit: true,
      responseType: 'json',
      onSubmit: function(file, extension){
        if (! (extension && /^(jpg|png|jpeg|gif)$/.test(extension))){
            alert("<%= t("upload_box.invalid_extension") %>: ." + extension);
            return false; //cancel upload
        }
        button.val("<%= t("upload_box.sending") %>...");
        this.setData({'authenticity_token'  : '<%= form_authenticity_token if protect_against_forgery? %>',
                      '_method': 'put',
                      'ajaxupload': true});
        this.disable(); },
      onComplete: function(file, response) {
        if(response['response'] == 'success'){
          image = frame.find("img");
          image.attr('src', response['url']);
          $("#destroy_upload_box").show();
        }else if(response['response'] == 'failure'){
          alert(response['message']) %>");
        }else{
          alert("<%= t("upload_box.error") %>");
        }
        button.val("<%= t("upload_box.edit") %>");
        this.enable()}
      });
  <% end %>
  });
  
});
<% end %>

<% attachment = object.send(field) %>
<% default_image_url = default_image_url_for(attachment) %>
<% image_url = image_url_for(object, field, klass_id) %>

<div id="frame_upload_box">

 <div class="frame"><%= image_tag image_url %></div>
 
 <% if default_image_url != image_url %>
   <%= button_to t("upload_box.edit"), "#", :id => "button_upload_box" %>
 <% else %>
   <%= button_to t("upload_box.new"), "#", :id => "button_upload_box" %>
 <% end %>

  
  <% unless object.new_record? %>
    <%= link_to_remote(t("upload_box.destroy"),
    :url => {:action => 'update'},
    :with => "'ajaxupload=true&_method=put&#{klass_id}[#{field}]=\"\"'",
    :html => {:id => "destroy_upload_box", :class => 'small', :style => "#{"display: none" unless attachment.exists?}"},
    :success => "$('#destroy_upload_box').hide();
                 image = $('#frame_upload_box').find('img');
                 image.attr('src', '#{default_image_url}');",
    :failure => "alert('#{t("upload_box.error")}')") %>
  <% end %>
</div>

<%= hidden_field(klass_id, field, :value => image_path_from_params(klass_id, field)) if object.new_record? %>

articles_controller.rb

class ArticlesController < ApplicationController
  before_filter :load_temp_upload, :only => ["create", "update"]

  def update
    if params[:ajaxupload]
      if @article.update_attributes(:picture => params[:article][:picture])
          render(:text => {:response => 'success', :url => @article.picture.url(:thumb)}.to_json)
        else
          render(:text => {:response => 'failure', :message => @article.errors.full_messages.join('\n')}.to_json)
        end
    else
      #...
    end
  end


  protected
  def load_temp_upload
    if !params[:article][:picture].blank? && params[:article][:picture].kind_of?(String)
      params[:article][:picture] = TempUpload.load(params[:article][:picture])
    end
  end
end

temp_upload.rb

class TempUpload
  
  attr_reader :path, :filename, :thumb_path, :uploaded_file
  
  def initialize(uploaded_file)
    @uploaded_file = uploaded_file
    
    @filename =  "#{Time.now.to_i}_#{@uploaded_file.original_filename}".gsub(/[^A-Za-z\d\.\-_]+/, '_') #timestamp to prevent duplicated file names and gsub for paperclip compatibility
    @path = File.join(TMP_UPLOAD_FOLDER, self.filename)
    @thumb_path = File.join(TMP_UPLOAD_FOLDER, 'thumb' ,self.filename)
  end
  
  def save
    save_original
    save_thumb
  end
  
  def save_original
    @uploaded_file.binmode if @uploaded_file.respond_to? :binmode
    tempfile = @uploaded_file.to_tempfile
    tempfile.close
    
    FileUtils.mkdir_p(File.dirname(@path))
    FileUtils.mv(tempfile.path, @path)
  end
  
  def save_thumb
    thumb_temp = Paperclip::Thumbnail.make(@uploaded_file, {:geometry => "60x60"})
    
    FileUtils.mkdir_p(File.dirname(@thumb_path))
    FileUtils.mv(thumb_temp.path, @thumb_path)
  end
  
  private :save_original, :save_thumb
  
  def url
    self.path.gsub(/^(.)*\/public/, '')
  end
  
  def thumb_url
    self.thumb_path.gsub(/^(.)*\/public/, '')
  end
  
  def self.load(filename)
    path = File.join(TMP_UPLOAD_FOLDER, filename)
    File.open(path) if File.file?(path)
  end
  
end

temp_uploads_controller.rb

class TempUploadsController < ApplicationController
  
  def create
    if params[:upload].blank?
      return render(:text => {:response => 'failure', :message => t('upload_box.no_file')}.to_json)
    end
    
    temp_upload = TempUpload.new(params[:upload])
    temp_upload.save
    render :text => {:response => 'success', :filename => temp_upload.filename, :thumb => temp_upload.thumb_url}.to_json
  end

end

temp_uploads_helper.rb

module TempUploadsHelper
  
  def photo_upload_box(object, field)
    klass_id = @controller.singular_class_name(object)
    
    render :partial => "temp_uploads/photo_upload_box", :locals => {:object => object, :field => field, :klass_id => klass_id}
  end
  
  def image_url_for(object, field, klass_id = nil)
    attachment = object.send(field)
    return attachment.url(:thumb) unless object.new_record?
    
    klass_id ||= @controller.singular_class_name(object)
    
    filename = attachment.original_filename
    filename ||= image_path_from_params(klass_id, field)
    
    if !filename.nil? && File.file?(file_path = File.join(TMP_UPLOAD_FOLDER, 'thumb', filename))
      file_path.gsub(/^(.)*public/, '')
    else
      default_image_url_for(attachment)
    end
  end
  
  def image_path_from_params(klass_id, field)
    (params[klass_id][field].respond_to?(:original_filename) ? params[klass_id][field].original_filename : params[klass_id][field]) if params[klass_id]
  end
  
  def default_image_url_for(attachment)
    attachment.send(:interpolate, attachment.instance_variable_get("@default_url"), :thumb)
  end
  
end