A method for acquiring images to perform aerial reconnaissance, implemented by an optical system located on board a mobile platform and having a line of sight, the optical system taking an image of an elementary region of ground, which is referred to as an elementary image (Im), for the acquisition of images during the implementation of said method, the following are defined: - an image acquisition mode referred to as planned mode, in which elementary images of a region of ground that is predefined depending on an operational need are acquired, said region being referred to as planned region, the acquisition being carried out in successive strips by moving the line of sight along a switchback path, a strip comprising one elementary image or a plurality of juxtaposed elementary images, characterised by the fact that the following are further defined for the acquisition of images during the implementation of said method: - an image acquisition mode referred to as opportunity mode, in which elementary images of at least one opportunity region are acquired, the opportunity region being located outside the predefined region of ground, said method comprising the following steps: A. acquiring, in the planned mode, a nominal planned region including a region of interest, B. interrupting the planned mode and acquiring, in the opportunity mode, elementary images of said opportunity region, C. resuming the planned mode, the line of sight being positioned so that the first elementary image acquired on resumption (Irep) belongs to the strip (B(k+1)) following the strip (B(k)) to which the last elementary image (Iint) acquired before interruption belongs, the acquisition time and/or the number of elementary images per strip being reduced, so as to cancel out a lag due to the opportunity acquisition, the elementary images being chosen so as to at least cover said region of interest, D. once the lag has been cancelled out, resuming the planned mode to acquire elementary images of the nominal planned region or region of interest, or newly acquiring elementary images, in the opportunity mode, of a new opportunity region. for the acquisition of images during the implementation of said method, the following are defined: - an image acquisition mode referred to as planned mode, in which elementary images of a region of ground that is predefined depending on an operational need are acquired, said region being referred to as planned region, the acquisition being carried out in successive strips by moving the line of sight along a switchback path, a strip comprising one elementary image or a plurality of juxtaposed elementary images, - an image acquisition mode referred to as planned mode, in which elementary images of a region of ground that is predefined depending on an operational need are acquired, said region being referred to as planned region, the acquisition being carried out in successive strips by moving the line of sight along a switchback path, a strip comprising one elementary image or a plurality of juxtaposed elementary images, characterised by the fact that the following are further defined for the acquisition of images during the implementation of said method: - an image acquisition mode referred to as opportunity mode, in which elementary images of at least one opportunity region are acquired, the opportunity region being located outside the predefined region of ground, - an image acquisition mode referred to as opportunity mode, in which elementary images of at least one opportunity region are acquired, the opportunity region being located outside the predefined region of ground, said method comprising the following steps: A. acquiring, in the planned mode, a nominal planned region including a region of interest, B. interrupting the planned mode and acquiring, in the opportunity mode, elementary images of said opportunity region, C. resuming the planned mode, the line of sight being positioned so that the first elementary image acquired on resumption (Irep) belongs to the strip (B(k+1)) following the strip (B(k)) to which the last elementary image (Iint) acquired before interruption belongs, the acquisition time and/or the number of elementary images per strip being reduced, so as to cancel out a lag due to the opportunity acquisition, the elementary images being chosen so as to at least cover said region of interest, D. once the lag has been cancelled out, resuming the planned mode to acquire elementary images of the nominal planned region or region of interest, or newly acquiring elementary images, in the opportunity mode, of a new opportunity region. A. acquiring, in the planned mode, a nominal planned region including a region of interest, B. interrupting the planned mode and acquiring, in the opportunity mode, elementary images of said opportunity region, C. resuming the planned mode, the line of sight being positioned so that the first elementary image acquired on resumption (Irep) belongs to the strip (B(k+1)) following the strip (B(k)) to which the last elementary image (Iint) acquired before interruption belongs, the acquisition time and/or the number of elementary images per strip being reduced, so as to cancel out a lag due to the opportunity acquisition, the elementary images being chosen so as to at least cover said region of interest, D. once the lag has been cancelled out, resuming the planned mode to acquire elementary images of the nominal planned region or region of interest, or newly acquiring elementary images, in the opportunity mode, of a new opportunity region.