Question about Mini_Magick and mogrify

Hi.

I'm trying to write a caption to an image in my Rails Project.

From http://www.imagemagick.org this is something I should use:

   width=`identify -format %w dragon.jpg`; \
   convert -background '#0008' -fill white -gravity center -size
${width}x30 \
           caption:"Faerie Dragons love hot apple pies\!" \
           +size dragon.jpg +swap -gravity south -composite anno_caption.jpg

If possible how can I write that in mini_magick? I thinks it's related to mogrify somehow.

Thanks.

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M.