After doing a little research, it seems that this feature isn't an option; at least from what I've read. Many other users also have a hard time trying to block Google images.
Try using OpenDNS
instead. It's free, though it does have a few ads, but it allows for you to use "phrase here" format to match exact phrases.
There's also a "VIP" paid version available. Obviously it has more features and removes ads, but the free version offers what you're looking for. Try that and if you have any more issues let us know!
Best of luck.