Where these projects actually succeed or stall

Not in the choice of vendor. In the rollout, which is the part nobody writes about because it is administrative rather than creative.

The four things that decide it

Whether someone wrote down the specification — background colour, crop ratio, camera direction — before contacting anybody.

Whether declining was made genuinely costless, stated by the employer, before the first person was asked.

Whether anyone counted how many people already have a usable headshot that is merely cropped wrongly. Frequently half, and it changes the size of the job.

Whether there is a process for person forty-one, joining in fourteen months.

What does not decide it

Image quality. By the time a company is choosing, the portraits have been judged good enough, and every product in the category clears that bar for an easy face.

The failure that looks like a vendor problem

A set with gaps in it. It is almost always a participation problem, and participation is a communication problem.