If you deleted the chat and chose to delete the media in the chat then you will lose them from the on-board memory.
Hi, Elvovo77 kindly be advised that you will only be able to restore your pictures if you had backed them up.
On your phone, please do the following:
1. From the home screen, swipe either up or down to access apps.
2. Select Google Photos.
3. Select the deleted picture then swipe up from the picture.
4. Tap Download.