If you attach the tablet to the computer using the charging cable it will install the drivers onto your computer then you can just go to the computer files folder and look at the nexus 7 by clicking on it. You will see the DCIM folder inside it is another folder called camera you can click on it to see your photos. From there just copy them onto the computer and you are done.
Depending on your device you may also be able to charge it from the computer while you are moving or copying photos. Note that if you move the images off of the tablet they will no longer be on it.