Did you take the picture yourself?
Try to retake the photo from Staples. Tell them that the photo you got from them was having issue as too dark or bright. Although I am not sure at Staples' policy, but in Shoppers we were told that we can retake the photo if it is being rejected by IRCC. Just keep the receipt.
I wouldn't recommend that, based from my personal experience... But your choice. Better to be safe than sorry. When the system flags your photo as too dark or too bright, get another photo. Just a recommendation, though.
Ask them to retake the photo for you, because they claim that they provide photos that fit the requirement. Otherwise, look for another reliable photo service and take another one. Sending a compliant photo is much better than crossing your fingers with one that can delay the process.
I got it clicked yesterday from London drugs. They check everything before giving it to you. I was initially having the same issue related to brightness but the photo from London drugs was without any problems.
London drugs do some testing named ICAO testing and if result is accepted, it confirms that your picture is fit for submission
