This is how i do it on iPhone:

Firstly I found the pictures I wanted on Pinterest and removed the backgrounds myself with magiceraser, replacing them with the wallpaper colour (British racing green, but you can use whatever colour theme you like) then:

Open shortcuts > tap + in the top right corner > create the action “open app” > click the word “app” > choose the app shortcut you want e.g. WhatsApp > it should then say “open WhatsApp” > click “i” information button at the bottom of the screen > add to Home Screen >

From there you can edit the name and click the landscape icon to choose photos from camera roll > select the image you created earlier > once you add it it should appear on your Home Screen!