What version of Android is it running? Anything above 4.2 (I think) requires that you confirm a computer's access via USB debugging. So you should get a popup on your phone asking permission to connect via USB debugging.

 

To my knowledge, all the USB debugging option is good for is to allow ADB (a very useful and powerful program in the Android Development Kit) the access it needs to perform some of the root/superuser-level functions it was built for. Also, since at least Jelly Bean (if not ICS), for security reasons, Android devices will only connect as media devices, instead of as removable drives as they once did. That's not to say that enabling the option won't help you with the problem you're trying to solve, though.

My first suggestion would be to enable your PC to show hidden files, then connect the phone to said computer, and look for a ".Trash1000" folder on the device. If the pictures haven't been deleted completely, they're likely in that folder.

If they aren't there, or that folder doesn't exist, the next step would be to get your hands on a data recovery program. Some flash memory manufacturers like SanDisk, PNY or Mushkin (to name a few) will sometimes offer the program for free, or very little ($5 USD or less). Usually, the programs are used to extract data off of a dead or dying flash drive/SD card/etc., but I've heard of them being used in similar situations to your own. Unfortunately, I can't help anymore than I have in that area, because each program is different depending on which manufacturer supplied it, and I have yet to use one, myself.

If your phone is rooted, you also have the options of using a file explorer app to search on the device itself for the ".Trash1000" I talked about earlier, or booting into a custom recovery (if one is installed) and connecting the phone via USB that way, which will allow the device to be seen as a removable drive. Just to be clear, I'm not saying that rooting the phone is necessary to solve this problem, only that it opens an extra door or two.

Good luck, and let me know if any of the suggestions help, or if you need me to clarify on anything.