There are several routes for physicians who want to perform disability exams.
Physicians can provide work injury or disability medical exams for a variety of clients. Clients can include attorneys, bureau of worker's compensation, employers, and insurers.

Some clients require that physicians who provide IMEs are trained and certified in disability examinations. There are several courses and certification tests that you can take.

Doctors who perform independent medical examinations are paid a fee for providing the exam and report to the client. If you perform IMEs, you will need to follow the template and/or answer questions requested by the client.

Courses and books:
Guide to the Evaluation of Permanent Impairment Sixth Edition
International Academy of Independent Medical Examiners training course
International Academy of Independent Medical Examiners study curriculum
SEAK onsite Independent Medical Exam training course
American Board of Independent Medical Examiners course

Certification/Exams:
American College of Independent Medical Examiners certification
International Academy of Independent Medical Examiners certification