I will complete Joseph's answer as I have been working on images in lesson issues.
- In Moodle 2.7 images in question text are imported (in lesson question page content) if you use Moodle XML format to export the question from the question bank and import them in lesson. Images in other fields are not imported because lesson don't support images in answers and responses. It is also possible to use my gift with media plugin to prepare your questions with images and import them in lesson (this plugin only support import and don't currently support export so it is not possible to use it to export questions with images from the question bank)
- In Moodle 2.8 available in November images in answer and feedback (imported in lesson "responses") are also imported. This is possible because lesson has been modified and there is now an editor with a filepicker for answers and responses when you create or edit questions in lesson.
- Multichoice question support images in content, answers and responses
- Matching questions support images in content and answers but not in Matches with answer (not possible as they appear in a select drop down)
- Essay question support images in content only. There is an issue in the tracker to add an editor for the teacher comments when he grade the student essays but this is a separate issue
- Numerical, True/False and Shortanswer questions support images in content and response. Additionally I think there is a bug and answer should be just a text field, not a textarea as it is now.
It was not easy to add images support to lesson, so please if you find something not working when Moodle 2.8 will be out, create an issue in the tracker.