Determine content-type for uploaded image

How do I determine the content type of the uploaded image? I have seen
that the default content-type is "application/octet-stream". What if I
wanted to upload a gif, bmp, jpg or other format. How will I determine
which format is uploaded?

Thanks.

How do I determine the content type of the uploaded image? I have seen
that the default content-type is "application/octet-stream". What if I
wanted to upload a gif, bmp, jpg or other format. How will I determine
which format is uploaded?

http://wiki.rubyonrails.org/rails/pages/HowtoUploadFiles

A ways down that page it says that the following will give you the content type (assuming a form with: <%= file_field "person", "picture" %>):

person['picture'].content_type

-philip