I'll assume that you can navigate the search function of the Getty Images app. Once you find the picture that you would like to use, tap on it, and it will fill the screen (see the image below). At the bottom of the screen tap the "send" button.
Once you have tapped the "send" button, a pop-up window will appear with a variety of options (see below). Select the html button (</>).
When you tap the html button, the pop-up window will change, and you will receive a message that the embed code has been copied to your clipboard.
Next you need to go to the WordPress app and start a new post or edit a draft. On the post interface there is an html button (see below).
Tapping the html button will change the look of the screen only slightly. You can tell that you are in html mode because the html button will be blue. Paste the html code that you copied from Gettys into this screen.
When you tap the html button again and return to the visual edit screen, the html code will disappear, and a placeholder will appear instead of the actual photo. To see the photo, which includes appropriate credit but no longer has a watermark, view your post or draft in browser mode or with a browser.