add git-annex-compute-imageconvert

doc/special_remotes/compute/git-annex-compute-imageconvert

@@ -0,0 +1,24 @@
+#!/bin/sh
+# git-annex compute special remote program that uses imagemagic's convert
+# to convert one type of image format into another. Eg, jpeg to gif.
+# 
+# Copyright 2025 Joey Hess; licenced under the GNU GPL version 3 or higher.
+set -e
+
+if [ -z "$1" ] || [ -z "$2" ]; then
+	echo "Specify the input image file, followed by the output image file." >&2
+	echo "Example: foo.jpg foo.gif" >&2
+	exit 1
+fi
+
+echo "INPUT $1"
+read input
+echo "OUTPUT $2"
+
+if [ -n "$input" ]; then
+	# Prefixing the filenames with "./" makes sure that they are processed
+	# as files, even if they look like dashed options.
+	mkdir -p "$(dirname "./$2")"
+	ln -s "$input" "./$1"
+	convert "./$1" "./$2"
+fi