You should not just infer consent. You should get express consent every time you take a photo.
While HIPAA does not specifically require consent to be attained if photos are to be used for clinical purposes (treatment, education and publication), there are some strict requirements relating to de-identification (discussed below) if you do not get consent. The American Health Information Management Association (AHIMA) takes a more practical approach and suggests informed consent should be sought.
Doctors often don't get consent, and when they do, they don't record it properly. A whopping 82% of the time, doctors don't document consent when taking a photo.
A study among dermatologists revealed that only 2% obtained written consent! While 46% received verbal consent, they failed to document this. A further 30% acquired verbal consent and documented it in the clinical notes, but they did not record it using an appropriate consent form.
We suggest you always obtain consent. The ease of distribution of digital images, the difficulty of properly de-identifying photos, and the grey area around when consent is required, in practice, means consent should be sought to cover yourself. Being able to point to documented consent may save grief should dispute arise in the future.