To display images included in the text of an object, templates often specify a maximum display size using the|image_reduire filter to limit their display size. Note that the display size can also be changed by passing a |largeur=xxx parameter to the insertion model.
Regardless of this size, the thumbnail of images whose original dimensions are larger than the value of the constant _IMAGE_TAILLE_MINI_AUTOLIEN have a link to display them in large size in the Mediabox. By default, the value of this constant is 800 pixels wide or high. It is possible to customise this value in your config/mes_options.php (See article dedicated to it).
Example :
// allow images that are more than 200px wide or high to be enlarged
define('_IMAGE_TAILLE_MINI_AUTOLIEN', 200);
It is possible to disable these automatic links by specifying a very high value:
define('_IMAGE_TAILLE_MINI_AUTOLIEN', 20000);