Honestly, I'm not sure I agree with this. Face recognition software uses patterns based off of the dimensions and angles of ones face. I'm not sure a simple picture would be enough to trick the system. A picture does represent an image of the target, it does not replicate the targets facial structure or dimensions in a 3d envirenment. Facial recognition software doesn't just use a picture of the person and match it with an existing picture, it also checks for things like eye spacing, nose angles, cheek definition, distance between chin and lips, lip curvatures, etc. Most software of this sort requires you to start out looking straight, then turn your head slightly right, left, then right again, then back to straight. While your doing this it is calculating all the key identifiers and dimensions of your face and matching those to what is saved from the original scan. That is hard to emulate with a picture. Maybe a picture will work for less complicated software, but if the op is going to go through the trouble of all this, I don't think he/she is going to buy the kmart special.
Now, I would be more worried about users being locked out due to tanning, (changes complexion of user), facial gesture not matching via smiling/not smiling it changes dimensions of face, weight gain or lose, etc.
Honestly, this is kind of a loaded question, really it all depends on the hardware and software capabilities of the product in question. Make sure you test the product before you buy it. Ask the developers if it uses 3d facial mapping, ask what its limitations are, does it do indepth comprehensive facial analysis, ie; does it check for width, length, depth, angles, etc. Does it check for background depth/vs facial placement. Most real facial recognition software (well what I consider to be real) will have these features. If the software doesn't use 3d mapping, and doesn't do point to point checks for unique key identifiers such as depth perceptions, distances, etc then look for something better.
When it comes to decisions like this you really get what you pay for. If you are trying to buy software only, and run the software with the built in camera, or a cheap external usb camera bought from staples or bestbuy then no, I would agree with Anders 100% and say anyone with a HD picture of the target would likely be granted access. If you plan on spending a lot of money and buy the whole system which includes a specialized camera that is made soley for this purpose, that has software that is specific to the camera designed to map the face correctly then I'd say yes, go for it.
It all comes back to how much are you willing to spend, and is that expense really worth it.
Sorry Anders, I see your post count and know you're a veteran, with extensive knowledge in computer science. I'm just not sure I agree with you on this answer 100%. While you are correct in your statement about using the picture, that is only applicable with low end to mid grade (FTS).