Error while assigning the content type

if request.post?
      @fData = params[:photo]
      puts("\n\n"+@fData.content_type+"\n\n\n") # Here I am getting
the right content type
      @fData.content_type = File.mime_type?
(params[:photo].original_filename)
      # In the above statement, I am getting the error while
reassigning the datatype. I am alrady using multipart in form
    # undefined method `content_type=' for #<File:C:/Users/dell/
AppData/Local/Temp/CGI55192-1>
    # {"photo"=>#<File:C:/Users/dell/AppData/Local/Temp/CGI55192-1>,
"picture"=>{"id"=>"0"}}
end