Great question. An iPad would be the most user friendly for the customer and long term cost effective.
Take your pick: a shared album link from Google Photos, iCloud Photos, a shared folder from Dropbox or any public website link.
Step 1: Follow the welcome wizard to setup the new iPad
Connect to WiFi and setup a separate Apple ID that's not connected to personal/work accounts.
If it's an existing iPad, I'd suggest backing up and doing a factory reset to wipe personal/work data.
Step 2: Use a passcode to secure Screen Time settings.
- Go to Settings > Screen Time
- Tap on Use Screen Time Passcode
Step 3: Restrict iPad to the Google Photos shared album
- Copy the Google Photos shared album link to the clipboard.
- Go to Settings > Screen Time > Content & Privacy Restrictions > Content Restrictions > Web Content > Allowed Website Only
- Paste in the Google Photos shared album link. Give the link a name.
Step 4: Guided Access keeps the iPad in a single app and allows you to control
- Go to Settings > Accessibility > Guided Access > turn on Guided Access.
- Open Safari and triple click the Home button.
[Optional] Step 5: Keep iPad screen always on
- Go to Settings > Accessibility > Guided Access > Passcode Settings
- Set Guided Access Passcode
- Open Safari
- Enable Guided Access: triple-click the Home button
- Bring up Options: triple-click the Home button again and enter your passcode
- Turn off the Sleep/Wake button.