How to add wallpaper from images stored in external source or folders in Android?

You can set any images as Wallpaper in Android provided they're stored in the "Pictures" folder in the main settings in Android. But if you want to add images stored in a different folder such as in Dropbox, Box, Google Drive folders, then do the following (in this example, I used images for this blog article from Android Foundry):

1. Open the image you would like to have as wallpaper from any of the sources, Dropbox, Box etc.,
2. Press the image once and you will see different options such as "Favorite", "Share", "Export" etc.,
3. Select the "Export" and choose the option "Save to SD Card" (even without the SD card it refers to internal storage)
4. Go to "Pictures" folder and save the image either in any of the existing folders or in "Wallpapers" folder (if there is no Wallpapers folder, you can create one using "create new folder" option).
5. Save the image in the new folder, here in this example it is stored in "Wallpapers" folder.
6. Go the main screen, press any blank space to see the "Add to Home Screen" options such as "Widgets", "Folders", "Wallpapers". Click the Wallpapers setting.
7. Choose the "Gallery" option and go to the "Wallpapers" folder created in Step 4 and adjust the screen size of this image and click "OK".

You will see something like this screen: