To delete a photo, find it in your Photos app and then tap 'Select' in the top right corner. Now, tap the bin icon in the bottom right corner and tap 'Delete photo.'
You can select multiple photos at once and then tap the bin icon to delete iphone photos selected.
If you've created your own folder of photographs and want to delete the whole thing, go to the Albums view and then tap 'Edit' in the top right corner. You can now tap the red circle that appears on the left to delete the album. You won't be able to do this with the default folders created by Apple.
In iOS 8, however, when you delete photographs by following the instructions above, they don't actually delete from your iPhone or iPad immediately. Instead, it moves the photos to the 'Recently Deleted' folder where it will remain for 30 days unless you go to the folder and delete it from there. This is handy when you accidentally delete a photograph, but if there's a photo you really want to remove from your iPhone or iPad you'll need to remember to delete it from here too here in erase photos from ipad also you can do this.
All you need to do is tap 'Select' and then tap 'Delete All' or select individual photos.
It's important to remember that, if you don't use iCloud and you back up your iPhone or iPad via iTunes, your most recent backup might contain the photograph you've deleted. Back up again once you've deleted the photos you don't want to overwrite it.