Follow the bundle of wires leading to the keyless module from below & to the left (clearly visible in your picture). There should be one that leads to a grey or black 2-wire male connector which is not connected to anything. It is probably partially/completely concealed behind the trunk carpet, so you may have to pull it down some to find the connector. It is often just in front of the inertia fuel cut-off switch. The wires going to this connector should both be white with a yellow stripe. (You may also find another unconnected grey or black female connector, but it will have 4 wires, and is NOT the one you want!) Once you've identified this connector, do the following:
1. Turn the key to RUN or ACC (leave the door open).
2. Take a large paper clip, screwdriver, or even a penny, and place it inside this connector so that it is touching both of the metal prongs in the connector at the same time. The connector is now shorted ("jumped"). All of your doors should then lock, and unlock.
3. Remove the paperclip/jumper.
4. Press any one button on the first transmitter you want to program, the doors should lock & unlock to verify programming.
5. Repeat step 4 for each additional remote you want to program, up to 4 total (don't forget the one attached to the key in the ignition).
6. When all transmitters have been programmed, turn the key to OFF. The doors should lock & unlock one last time.
7. Check to make sure all the transmitters work. Repeat programming if any don't work. You will have to re-program any custom keyless code you may have had, as well as reset the autolock feature to your desired option.
Note that any time you do this you have to program all of the transmitters at the same time. Each time you enter programming mode with the jumper, it erases the module's memory.
Good Luck!