If you want to delete a whole bunch of pictures from your Camera Roll, your Photos app has a group selection tool. This gives you the ability to bulk remove photos by selecting groups of images by their date.
With this tool you no longer have to tap and mark individual pictures. Here’s how to do it:
Go to your Photos app
Click on the tab marked Photos on the bottom
Select each date (in the upper right corner) to delete those images taken in each date group
Tap the Trash icon in the lower right corner
You can deselect individual photos and prevent them from being deleted by taping on the blue circle on the bottom right corner of each photo.
TIP: Be sure you’ve backed-up your photos or that you really never want to see them again, because you can’t undo the deletion.