An inspection system for inspecting an interior surface of a pipeline has a frame adapted to travel in the pipeline and an imaging means for imaging a selected portion of the interior surface of the pipeline. The imaging means has a field of view and is mounted in a rotatable manner on the frame. The inspection system has with a two-dimensional pattern generator for generating a two-dimensional pattern projection. The generator is mounted with the imaging means to project the two-dimensional pattern projection in the field of view thereof. The imaging means provide images of the selected portion of the internal surface comprising the two-dimensional pattern projection for monitoring a perpendicularity of the optical axis of the imaging means with respect to the selected portion of the interior surface of the pipeline thanks to a shape of the two-dimensional pattern projection prior to inspection of the internal surface.