Update license file

img/backgrounds/COPYING

@@ -1,19 +1,24 @@
-The following pictures located in this folder:
+The following pictures contained in this folder
 
-1.jpg
-2.jpg
-3.jpg
-4.jpg
-5.jpg
-6.jpg
+https://stocksnap.io/photo/house-interior-ZZ1IHRDEML
+https://stocksnap.io/photo/interior-design-BY59S6FSEP
+https://stocksnap.io/photo/abstract-background-RKQU798YK0
 
-Are licensed under the Unsplash license. More information
-at https://unsplash.com/license
+are licensed under CC0 1.0 Universal (CC0 1.0)
+Public Domain Dedication. More information
+at https://creativecommons.org/publicdomain/zero/1.0/
 
-The images can be found at the following links
-https://unsplash.com/es/fotos/1hlFqUdFv1s
-https://unsplash.com/es/fotos/QMDap1TAu0g
-https://unsplash.com/es/fotos/NRQV-hBF10M
-https://unsplash.com/es/fotos/17NCG_wOkMY
-https://unsplash.com/es/fotos/qtRF_RxCAo0
-https://unsplash.com/es/fotos/KnLj3o9A66E
+---
+The following pictures contained in this folder
+https://commons.wikimedia.org/wiki/File:Wooden_footbridge_in_Shinjuku_Gyoen_National_Garden,_Tokyo,_Japan,_a_sunny_day_with_blue_sky.jpg
+https://commons.wikimedia.org/wiki/File:Long_Room_Interior,_Trinity_College_Dublin,_Ireland_-_Diliff.jpg
+https://commons.wikimedia.org/wiki/File:La_Fenice_Opera_House_from_the_stage.jpg
+https://stocksnap.io/photo/beach-summer-0M1SPKYTR4
+
+are licensed under the Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license. More information at https://creativecommons.org/licenses/by-sa/4.0/deed.en
+
+---
+The following picture contained in this folder
+https://images.nasa.gov/details/iss036e005944
+
+is licensed under https://www.nasa.gov/multimedia/guidelines/index.html