File upload does not work using:
form.file_upload_with(:name => 'image[1]').file_name = '/tmp/image.jpg'
form.submit
This is an out-of-date example: https://github.com/sparklemotion/mechanize/blob/master/examples/flickr_upload.rb
I tried this on two different sites.
I'm using Mechanize 2.6.0.