Dashboard: Add photo credits and background picture requirements to Readme

Signed-off-by: Jan C. Borchardt <hey@jancborchardt.net>

apps/dashboard/README.md

@@ -1,5 +1,33 @@
 # Dashboard
 
-Picture credit:
-- [Clouds by Kamil Porembiński](https://www.flickr.com/photos/paszczak000/8715851521/)
-- [Un beau soir dété by Tanguy Domenge](https://www.flickr.com/photos/148302424@N05/36591009215/)
+
+## Background picture credits
+
+- Default background: [Clouds (Kamil Porembiński, CC BY-SA)](https://www.flickr.com/photos/paszczak000/8715851521/) – original 4k, color modified and sky color changed to Nextcloud blue.
+- Default dark mode background: [Pedra azul milky way (Eduardo Neves, CC BY-SA)](https://commons.wikimedia.org/wiki/File:Pedra_Azul_Milky_Way.jpg) – original 5k.
+- [Butterfly wing scale (Anatoly Mikhaltsov, CC BY-SA)](https://commons.wikimedia.org/wiki/File:%D0%A7%D0%B5%D1%88%D1%83%D0%B9%D0%BA%D0%B8_%D0%BA%D1%80%D1%8B%D0%BB%D0%B0_%D0%B1%D0%B0%D0%B1%D0%BE%D1%87%D0%BA%D0%B8.jpg) – original 5k, cropped to use top right and retouched away a bright spot, now 4k.
+- [Cetonia aurata take off composition (Bernie, Public Domain)](https://commons.wikimedia.org/wiki/File:Cetonia_aurata_take_off_composition_05172009.jpg) – original 8k.
+- [Ribbed red metal (Dejan Krsmanovic, CC BY)](https://www.flickr.com/photos/dejankrsmanovic/42971456774/) – original 5k.
+- [Barents bloom (European Space Agency, CC BY-SA)](https://www.esa.int/ESA_Multimedia/Images/2016/08/Barents_bloom) – original 2k (it’s fine since the motive is blurry anyway), rotated 90° right.
+- [Flippity floppity (Hannes Fritz, CC BY-SA)](http://hannes.photos/flippity-floppity) – original 4k, cropped to top left (2k) so the sharp parts are not part of the photo, looks better.
+- [Roulette (Hannes Fritz, CC BY-SA)](http://hannes.photos/roulette) – original 4k.
+- [Sea spray (Hannes Fritz, CC BY-SA)](http://hannes.photos/sea-spray) – original 6k.
+- [New zealand fern (Bernard Spragg, CC0)](https://commons.wikimedia.org/wiki/File:NZ_Fern.(Blechnum_chambersii)_(11263534936).jpg) – original 2.5k.
+- [Pink tapioca bubbles (Rawpixel, CC BY)](https://www.flickr.com/photos/byrawpixel/27665140298/in/photostream/) – original 6k.
+- [Waxing crescent moon (NASA, Public Domain)](https://www.nasa.gov/image-feature/a-waxing-crescent-moon)
+- [Cityscape (Tommy Chau, CC BY)](https://www.flickr.com/photos/90975693@N05/16910999368) – original 6k.
+- [Lion rock hill (Tommy Chau, CC BY)](https://www.flickr.com/photos/90975693@N05/17136440246) – original 6k.
+- [Yellow bricks (Lali Masriera, CC BY)](https://www.flickr.com/photos/visualpanic/3982464447) – original 4k, color modified for visibility of icons, and slightly cropped on the left so motive is centered.
+
+
+## Background picture requirements
+
+A reference to why it was very difficult to actually find good background pictures – there are quite some requirements when it comes to picking:
+
+- It needs to be an exceptionally good photo of course – since when chosen, people will see it every day.
+- We need to have a good balance of different motives, e.g. not too many landscape pics.
+- Same for a good balance of different colors.
+- The photo needs to work as a background. Photos with objects focused in the middle don’t really work as they will be overlapped by the widgets anyway.
+- Especially the top part can’t have too much differing contrast, as then it’s not possible to see the navigation icons.
+- We serve the pictures at 4k resolution and most of the selected images are also available in 6k or higher so it is future-proof.
+- For the search of course we had to limit to CC0, CC By and CC By-Sa. Only CC0 would have been practically impossible cause there’s just not so many good ones which fit.