This is good advice, don't get me wrong (I read the article), but you don't absolutely have to have a pro photo. What you do need is a good, clear headshot. Advice like yours is necessary because I've seen a lot of really bad, unprofessional LI photos:

1/ Don't use your Facebook profile photo

2/ Don't use anything blurry: photo should be well lit and clear

3/ Don't use a photo that isn't a headshot—make sure your face is clearly visible and smiling

4/ Don't use anything where you're engaging in unprofessional behaviour