Photos app take up 2.5GB when I have no photos

If your iPad continues to indicate that storage space is occupied by photos - and all have been cleared from the Recently Deleted folder - try a forced restart of your iPad:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If the problem persists after performing the restart, it may be necessary to fully reset your iPad. Before proceeding, ensure that you have a current iCloud or iTunes backup before performing the reset:

How to back up your iPhone, iPad, and iPod touch - Apple Support

When you are happy to proceed, you can reset the iPad from settings:

Settings > General > Transfer or Reset iPad > Erase All Content & Settings

After the reset, you will need to setup the iPad using your AppleID credentials. During setup, you will have opportunity to restore your data and settings from your backup.

Photos deleted from iCloud continue to occupy space - permitting recovery for up to 30 days.

If your iPad is not using iCloud Photos, deleted photos remain within the Photos Recently Deleted folder until they are also removed from this folder - either manually, or automatically after 30 days.

To manually remove photos from this folder, open the Photos App - then open Recently Deleted from the sidebar; tap Select at top-right of the Photo App Window, then tap Delete All at bottom-left.