On your computer:
1) Right Click on the image
2) Select "Save Image As"
3) Leave the ".jpg" file type as it is
4) Select the folder you want it in
5) Select a helpful name, type it in leaving the ".jpg" letter alone
6) Press the "Save" button
On your Iphone or Ipad:
1) Long press on the image
2) Choose from the menu items, perhaps,
 "Add to Photos"

Android is similar.
To utilize any of these images royalty free do the following: