gistfile1.rb

# Create a new image
ruby-1.9.2-p136 :120 > image = Image.new()
 => #<Image id: nil, table_name: nil, table_id: nil, title: nil, description: nil, tiny: nil, small: nil, medium: nil, large: nil, original: nil, dcreate: nil, asset_file_name: nil, asset_content_type: nil, asset_file_size: nil, asset_updated_at: nil, asset_remote_url: nil> 

# Set a style dynamically
ruby-1.9.2-p136 :126 > image.asset.styles[:large] = Paperclip::Style.new(:large, '300x300#', image.asset)
 => #<Paperclip::Style:0x00000100f0f5e0 @name=:large, @attachment=/assets/original/missing.png, @geometry="300x300#", @format=nil, @other_args={}> 

# Add a new asset and BOOM
ruby-1.9.2-p136 :127 > image.asset = File.new(Rails.root+'public/images/rails.png')
sh: line 1:  3445 Trace/BPT trap: 5       identify -format %wx%h '/var/folders/vk/zb0rt8tx37v5x3jkvsrvjh1w++++fr/T/stream20110302-1569-1wzjw20.png[0]' 2> /dev/null
 => #<File:/Users/vinnie/Projects/groundctrl/public/images/rails.png> 

did you solved this problem?