Google Takeout makes it easy to download all your Google Photos in a few clicks. On the next screen, scroll down to Export your data, click the downward facing arrow in that section, and then click the Backup link as pictured here. To get everything from Google Photos, login to the service and click the Settings cog icon in the upper-right corner.
Start from the Google Photos settings to download all your images. Download every picture from Google Photos IDG
