I own a couple of foscam Pan Tilt (no Zoom) webcams which i have bought under different brand names, some are Watchbot and one is from the Aldi sold as Supra IPC-1A. The webcams are indoor types, so they are inside looking out through the window. At daytime they work just fine, but when it gets dark they have a sensor which switches on the Infrared Leds to have a better view in low light.
The problem is that they are behind glass, so the IR bounces back en completely blinds the webcam as you can see from the picture: 
Although this webcam supposed to have IR Led control from the GUI, in 90% of the time this didn’t work; so i decided to solve this permanently. The photo on the left shows the front of the webcam with the lens, IR Leds and the LDR (Light Dependant Resistor) which is responsible for measuring the light and switching on the IR Leds when it gets to dark.
To disable the Infrared Leds we have to disassemble the camera head. Find a small philips screwdriver and remove the two screw which key the camera head together. Be careful with the screws, when they fall, you most likely will never find them again 🙂
When the screws are loose, you can carefully pry the parts apart.
My webcam now shows a PCB with the camera logic. The with cable on the top is for the connection to the LED and LDR board, i disassembled it further, but there is no need to do so if you only want to enable the IR Leds.
The only thing that you need to do is disconnect that small white cable as shown in the picture below and then reassemble the head. This way you can easily undo the operation in the future if you need to.
Now reconnect the webcam to power and verify that it’s working OK.
Older model Foscam webcams
The image below is from a different kind of foscam webcam, where everything is attached to one single board attached to the motor driven axis. The way to fix this type is also to remove the screws and also unscrew the lens all the way. After that the PCB with everything is accessible and you can fix the IR Leds going on by short circuiting the LDR (low resistance is lots of light). See the image for the idea. By only twisting the LDR, you can simply undo this mod when you want to.
After you reassemble the webcam head and screw in the lens, you will have to refocus to get a good picture again.
Have fun!