Filter to turn figure titles into short captions in LaTeX

latex-short-captions.lua

-- don't do anything unless we target latex
if FORMAT ~= "latex" then
  return {}
end

local List = require'pandoc.List'

local function latex(str)
  return List:new{pandoc.RawInline('latex', str)}
end

local function is_titled_figure(para)
  return #para.content == 1 and
    para.content[1].t == "Image" and
    para.content[1].title
end

local function read_inlines(txt)
  return pandoc.read(txt).blocks[1].content
end

local function make_caption(long_caption, short_caption)
  return latex'\\caption['
    .. short_caption .. latex']{'
    .. long_caption .. latex'}\n'
end

local function figure_with_short_caption(para)
  if not is_titled_figure(para) then
    return nil
  end
  local img = para.content[1]
  local title_inlines = read_inlines(img.title:gsub('^fig:', ''))
  return pandoc.Plain(
    latex'\\begin{figure}\n\\centering\n'
      .. {img}
      .. latex'\n'
      .. make_caption(img.caption, title_inlines)
      .. latex'\\end{figure}'
  )
end

return {{Para = figure_with_short_caption}}

Your filter works great with single figures. But it will throw errors having subfigures.

See pandoc/lua-filters#62