How to determine each PSP model without any version information
If you are unfamiliar with PSPs, but want to buy a new one, you should be able to distinguish the different PSP types, so you don't run into bad surprises, when you discover that you bought the wrong PSP version. This is especially useful on bazaars, where you don't have the time and possibility to quickly google what you need to look for.
Let's start with the easiest one. You will never mistake this one for another PSP version.
Now that is easy.
First and foremost, the easiest way to spot a 1000 on first sight are the speaker locations. This is the only model that has them on the lower part of the console. The speakers are behind those two holes that are on both sides of the PSP. In the pictures you can see one hole between the analog stick and the home button and the other one is right above the start button.
Another unique property of the PSP-1000 are the slightly punched in dots on the upper side of the PSP.
The back of the PSP-1000 is always matte (except it is using a custom aftermarket shell). It also has a large ring around the PSP logo. On the right side, you can partially see the Memory Stick slot, below the MagicGate label.
The PSP-1000 is the only one that has a dedicated button for opening the UMD drive. In the above picture this button is seen on the right side, with the label OPEN on it. This PSP generation is additionally the only one, that support data transmission over infrared. The infrared interface is the black (actually red, if you look at it closely) spot between the L button and the USB port.
This PSP is also the only one that has these two additional contacts where the DC input is. All future generations lack these two contacts and have only the circular DC input. The input is seen in the picture above, on the left side, coloured in yellow.
Here you can see the left side of the PSP. The PSP-1000 is the only one with such a memory card slot. It is partially on the back and not on the side, entirely, like in later generations. In the above picture, you can see the memory card slot below the WLAN switch, which is roughly below the analogue stick, from the photo observant's perspective.
You can also see it partially on the picture that shows the PSP-1000's back. It is on the right side, with the label MagicGate above it.