My iPhone is over capacity. Is there a way to remove specific data from an iPhone Backup?
Well since you are using Mac OSX, when you plug in your phone you can do the following to back up your pictures OUTSIDE of iTunes.

Step 1

Open up Preview with your phone plugged in. Go to File > Import Image. You will see it populate all your photos/videos. Save them in a separate folder (maybe somewhere on your desktop), then delete them all from your phone.

If you are concerned about mass deleting these files, you can just do it with SSH. This is after you've imported all your images through preview.

From Terminal on your desktop type 

ssh root@your-iphones-ip-address-here


Will prompt you with a PW, chances are if you haven't changed it it's alpine or Alpine. Change directories via the following command: 

cd /var/mobile/Media/DCIM


Depending on the amount of images/videos you have you will see 100APPLE/ and maybe 101APPLE/. In the directory type this to remove ALL images and movies in one command

rm -r 100APPLE/ 
rm -r 101APPLE/


Backup in iTunes now and you have a fresh backup with just numbers/apps/whatever else. You can then import the pictures/videos back if you want after you restore it.