An app which enables healthcare professionals to share photos is to be rolled out across western Europe by the end of the year.
The app was designed to enable doctors to share pictures of their patients, both with each other and with medical students.
So far, more than 150,000 doctors have uploaded case photos with the patient's identity obscured.
However, some experts have expressed concern about patient confidentiality. Patients' faces are automatically obscured by the app but users must manually block identifying marks like tattoos.
Each photo is reviewed by moderators before it is added to the database.
Founder Dr Josh Landy told the BBC that the Figure 1 service did not access any patient records.
"We do not possess any personal medical data at all. The best way to keep a secret is not to have it. We are not an organisation that delivers healthcare," he told the BBC.
But doctors must provide identifying credentials and are also advised to notify their employees and patients to find out about consent policies.
"Legally, we found that identifying the doctor does not identify the patient," said Dr Landy.
"However some [medical] conditions are so rare that they can't be posted. One user wanted to post something but there are only seven cases of it in the US and they had all been reportable because they are rare, so the patient could have been identified."
Anybody can download the app for free, but only verified healthcare professionals can upload photos or comment on them, he added.