I don't think the USB connector puts out enough power for an LED flash. A status LED yes, but not one bright enough to help with photos.
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thanks for the reply, yes, I tried it by two 5mm white leds, it worked but it was not enough to take better photos, plus, leds color is a bit unnatural and didn't like it, so I was thinking on a simple 6v 1watt lamp (didn't know how they're called), they took high amp so the usb port was unable to provide it, finally, I realized that these lamps (photo attached, again, I didn't know the name of it) take less current and they're more suitable for this job, and they're heavy duty!
edit: I think they're called xenon lamps.