I wouldn't log in on any computer that I didn't strongly trust. Keyloggers are everywhere these days. I would recommend buying a high-definition webcam off Amazon for like $50 instead.
i think for one photo is enough a cheap webcam for 10$. Also you can log in from your smartphone/tablet and take a photo with front camera
If you read the post above, you can't do that. Poloniex won't recognize the camera. In time, Poloniex will probably release a mobile app that is compatible with smartphone cameras like Coinbase did, but in the meantime, it's easiest just to get a decent webcam.
If you can find a webcam for $10, I doubt it's much higher quality than a built-in cam. I'd rather pay $40-50 for a well-rated 720p or 1080p web cam than risk wasting time on a cheap knockoff.