In the license files CC-BY-4.0.txt, CC0-1.0.txt, and GPL-3.0-or-later.txt, the text looks mostly the same as the plaintext from the licenses' official sources (CC BY 4.0, CC0 1.0, GPL 3.0) -- except for the spacing.

Some differences are stylistic (indentation, centering) and others are clear errors (missing blank lines, misplaced carriage returns, and extra spaces in the middle of a URL).

So, would it be better to change the license files to exactly match the copy/pasted official plaintext? Or should these files be left as is? Or some third option?

Using reuse lint the following files have no license:

Makefile
README.md
.git
img/cat.jpg
img/dog.jpg
src/main.c

I had to remove colons to detect licenses, for example:

<!--
SPDX-Copyright: 2019 Jane Doe <[email protected]>

SPDX-License-Identifier: GPL-3.0-or-later
-->

into

<!--
SPDX-Copyright 2019 Jane Doe <[email protected]>

SPDX-License-Identifier: GPL-3.0-or-later
-->

Using reuse, version 0.3.4 on Linux Ubuntu 16.04.

Steps to replicate

1. checkout this repository
2. call reuse lint in root directory

Should be fixed with #6 and #7