Fixes #7992 #2

	name: Image metadata check CI

	on:
	push:
	branches: [ master ]
	paths: [ '.webp', '.png', '.jpg', '.jpeg' ]
	pull_request:
	paths: [ '.webp', '.png', '.jpg', '.jpeg' ]

	permissions:
	contents: read

	jobs:
	build:
	name: Image Metadata
	runs-on: ubuntu-latest
	env:
	BASE_SHA: ${{ github.event_name == 'push' && github.event.before \|\| github.event.pull_request.base.sha }}
	HEAD_SHA: ${{ github.event_name == 'push' && github.event.after \|\| github.event.pull_request.head.sha }}

	steps:
	- name: exiftool installation
	run: \|
	sudo apt-get install --assume-yes exiftool

	- uses: actions/checkout@v4
	with:
	fetch-depth: 0

	- name: check image metadata
	run: \|
	mapfile -t image_files < <(git diff --name-only --diff-filter=d "$BASE_SHA" "$HEAD_SHA" \| grep -E '\.(webp\|png\|je?pg)$')
	# cycle through the changed image files, make sure they have the right fields
	for file in "${image_files[@]}"; do
	# check Artist tag, fail if missing
	artist="$(exiftool -p '$Artist' "$file")"
	if [ "$artist" ]; then
	printf 'Artist tag in %s is %s\n' "$file" "$artist"
	else
	printf 'no Artist EXIF tag in %s\n' "$file"
	exit 1
	fi
	# check Copyright tag, fail if missing or wrong type
	copyright="$(exiftool -p '$Copyright' "$file")"
	case $copyright in
	'GNU GPL v2+'\|'CC BY-SA 4.0'\|CC0)
	printf 'Copyright tag in %s is %s\n' "$file" "$copyright"
	;;
	'')
	printf 'no Copyright EXIF tag in %s\n' "$file"
	exit 1
	;;
	*)
	printf 'Copyright tag %s in file %s is not an accepted license! Must be one of: "GNU GPL v2+", "CC BY-SA 4.0", "CC0"\n' "$copyright" "$file"
	exit 1
	;;
	esac
	done

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