File object treated as a string

I am trying to implement the uploading of a file to a remote server

My upload form looks like this:

<%= start_form_tag(:action => “save_image”, :multipart => true) %>

Description <%= text_area("image", "descript", "cols" => 33, "rows" => 5) %> Image <%= file_field("image", "picture", "size"=>"30") %> <%= submit_tag(" SUBMIT ") %>

<%= end_form_tag %>

This links to “save_image” action in the controller. Controller looks
like this:

    def save_image
            @image = Image.new(params[:image])
            # attempt to save entry in the db
            if @image.save
                    # info saved in db OK. Save file on the server
                    write_file(params[:image])
                    redirect_to(:controller => 'shto', :action => 

‘index’)
else
render(:action => :get)
end
end

    def write_file(uploaded_file)
                    uploaded_file['picture'].rewind
                    File.open("pictures/upload/#{@image.id}.#{@image.extention}", 

“wb”) { |f| f.write(uploaded_file[‘picture’].read) }
end
end

My image model looks like this:

class Image < ActiveRecord::Base

    def picture=(image_field)
            extname_dot = File.extname(image_field)
            self.extention = extname_dot.slice(1, 

extname_dot.length)
self.submitDate = Time.now
end
end

When I click the submit button on the form, it saves the image entry in
the database OK, but errors while trying to write the file to the
server. The error I get is the following:

undefined method `rewind’ for #String:0x2aaaad062eb8

It seems to be treating uploaded_file[‘picture’] as a string instead of
a File object. I tried implementing this with Agile web development
rails book, and also tried using other examples on the web, it always
comes down to this issue. Perhaps I am missing something, or this has to
do with my ruby version or the fact that I’m running this on Apache…

Any help would be greatly appreciated.

Thanks!

…Ed