[theme-reviewers] How to license images in themes?

[Nicolas GUILLAUME]

Hi,
I understand that all ressources in a theme have to be GPL compatible.
I am intending to use personal pictures and/or pictures from a 
photographer in my theme.

I have checked around some of the WP directory themes using images and 
found different practices in the readme file :
1)  nothing mentioned  at all about images
2) link to a forum where image author grants full freedom for the use of 
the image (wihtout mentioning the GPL license)
3) theme author saying that all theme images are its personal creation 
and are free for personal and commercial use

So my question is*: what is mandatory about theme image license in the 
readme.txt in the following cases*  ?
1) Personal pictures from theme author
2) Images not created by theme author

Thanks!
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