To delete a photo in your Discover feed -
1) Click on the image
2) Click the menu (the three dots) in the top right
3) Click "Delete"
To delete a photo you have saved,
1) Click the profile (person) icon in the bottom navigation to get to your saved images
2) Click on the image
3) Click the "trash can" icon in the bottom of the screen
Please reach out if you have any additional questions!