For many years a regular feature of the box art on LEGO sets were photographs of possible Alternate models to the stock model featured (for which instructions are provided). These alternate builds were created by designers but instructions were not usually provided. A notable exception are some Creator sets which provide instructions for multiple builds from the same set (unlike an idea book which provides many ideas and instructions for building without reference to any specific set.)
In the early 21st Century LEGO stopped using such images on the box art. Photos and computer-generated renderings on sets began to feature the play features and details of the stock model. Fan speculation has been that this change was both a shift in marketing tactics and a response to complaints from parents who could not find instructions for their child to follow for the alternate models.
In 2011 the website Rebrickable went online which shares fan-created alternate models and a function which allows a user to enter multiple sets and see what stock models or MOCs can be built from the elements one owns.