How to take screenshots without using buttons?
Another way to take screenshot without hardware inputs (physical buttons) would be to do so with software inputs (on-screen buttons).  I remember using a software to capture images and videos of my phone a few years ago.

Samsung Galaxy comes with gesture software that is embedded to the OS that a user can slide edge of one's hand across the screen to take screenshots; but I am not sure if it is available to Motorola phones as it seemed like an extention that Samsung added to the Android.

You should be able to find a number of screen capture applications if you search for "screen capture" in Play Store.  They usually display a floating icon or a notification bar icon that you can touch to capture screenshots.