There is actually another, cleaner way to achieve this; and it is even somewhat documented in the official wiki: How To: Move version name to end of filename, instead of front
Using this method your version code would look like this:
version :gif_preview, :if => :is_gif? do
process :remove_animation
process :resize_to_fill => [555, 2000]
process :convert => 'jpg'
def full_filename(for_file)
super.chomp(File.extname(super)) + '.jpg'
end
end
def remove_animation
manipulate! do |img, index|
index == 0 ? img : nil
end
end