The only method I have found to do this is to open up Image Capture, import all photos somewhere you can easily delete them from (e.g. a new folder on your desktop) but ensure that you have 'Delete after import' box checked so that they are deleted from the iPad as the import happens. Hey Presto!
Sorry, bad answer, but sliding your finger makes it a little easier.
Go to the folder with the photos you want to delete on your iPad, then tap the icon in the top right (box with an arrow in it) then hold on one of the photo till you see a check mark appear on it. Then you can tap, or slide your finger along the photos you want to select, then press the red delete button at the bottom.
this works pretty quickly actually. that's how i delete multiple pics
Isn't there an option to select multiple photos and delete them all at once in iOS 5? I don't have my devices with me at the moment so I can't check but I'm pretty sure you can... Maybe that's just within an album though.
Try to use ifunbox software and find the pics on ipad var dir. You need to dl afc2add from cydia too, hope this will help you.
If you are sure you have all your pictures backed up to your pc and not just in iTunes, then there is another way. Not any easier, just another way :-) Once you have connected your iPad to the pc and the backup is done, in windows explorer navigate to your ipad. (my windows 7 automatically brings this up when I connect) Go to the internal storage. You will see a folder named DCIM. Open this folder and it will contain folders with alpha-numerical names each of these will contain a different set of pictures. Find the ones you want to delete and delete that folder. Or just individual ones. If you have the iPad set to sync with a particular folder, I just created a folder in mypictures call iPad pics and pointed it to sync there. That way I can control the folders and pics on my iPad from there.
you can jailbreak your iPad to get an app that allows you to select multiple photos or albums and delete them