ruby on rails - Mechanical Turk: Post file to externalSubmit interface? -

I have set up my own custom form for mechanical torque and am posting on my external interface.

  & lt; Form enctype = "multipart / form-data" action = "https://workersandbox.mturk.com/mturk/externalSubmit" method = "post" name = "mturk_form" id = "mturk_form" & gt; & Lt; P & gt; & Lt; Label for = "turk_task_image_image" & gt; Upload an image & lt; / Label & gt; & Lt; Br> & Lt; Input type = "file" size = "30" name = "turk_task_image [image]" id = "turk_task_image_image" & gt; & Lt; / P & gt; & Lt; B & gt; - OR - & lt; / B & gt; & Lt; Br> & Lt; Br> & Lt; P & gt; & Lt; Label = "turk_task_image_url" for & gt; Specify an Image URL & lt; / Label & gt; & Lt; Br> & Lt; Input type = "text" size = "30" name = "turkey_task_image [url]" id = "turk_task_image_url" & gt; & Lt; / P & gt; & Lt; P & gt; & Lt; Label = "turk_task_image_description" for & gt; Details (optional) & lt; / Label & gt; & Lt; Br> & Lt; Textarea rows = "3" name = "turkey_task_image [details]" id = "turkey_task_image_details" cols = "80" & gt; & Lt; / Textarea & gt; & Lt; / P & gt; & Lt; Input type = "hidden" value = "ASSIGNMENT_ID_NOT_AVAILABLE" name = "assignment id" id = "assignment id" & gt; & Lt; Input type = "hidden" value = "200" name = "work [storyboard_space_id]" id = "task_storyboard_location_id" & gt; & Lt; Input type = "hidden" value = "36" name = "work [turk_task_id]" id = "task_turk_task_id" & gt; & Lt; P & gt; & Lt; Input type = "submit" value = "You must accept the hit before submitting the result." Name = "commit" id = "submitbutton" disabled = "" & gt; & Lt; Img border = "0" style = "display: none;" Src = "/ images / spinner.gif? 1274319066" id = "spinner" alt = "spinner" & gt; & Lt; / P & gt; & Lt; / Form & gt;  

When I retrieve the responses, all text field values ​​are available but there is no posted file. According to API documents, should I get another URL that should be uploaded to the uploaded file?

How do I get the URL posted on the external URL interface?

One note, I am using RTKK gem to make these HITs. But about the support for uploaded files, I do not see anything in the code.