Method for image acquisition of an object in transit on a movable supporting surface, comprising the following steps: - arranging at least one optical device for image acquisition comprising a respective linear camera associated with a lighting device; - detecting a presence signal of said object in a preset position on said movable supporting surface, and signals indicating at least one dimension and/or the position of said object on said movable supporting surface, said signals being generated by at least one sensor (6; 7) arranged upstream of said linear camera in the advancing direction of said movable supporting surface; - detecting a "trigger event" signal, generated on the basis of said presence signal, said linear camera starting to acquire an image of said object on the basis of said "trigger event" signal; - starting to acquire an image of said object by said linear camera, when said object has travelled a preset distance from said preset position, said distance depending on said at least one dimension of said object and/or on the position of said object on said movable supporting surface, said distance being calculated by an advance sensor associated with said movable supporting surface, said advance sensor being suitable for generating a signal comprising an electric pulse at each preset movement of said movable supporting surface, said advance sensor being operationally connected to said linear camera, or to a control device that controls said linear camera, characterised in that it further comprises: - setting a mode for image acquisition of said linear camera on the basis of the resolution of said advance sensor, said setting comprising selecting said acquisition mode from a plurality of different acquisition modes, said resolution consisting of a distance travelled by said movable supporting surface in the time that elapses between two successive pulses generated by said advance sensor. - arranging at least one optical device for image acquisition comprising a respective linear camera associated with a lighting device; - detecting a presence signal of said object in a preset position on said movable supporting surface, and signals indicating at least one dimension and/or the position of said object on said movable supporting surface, said signals being generated by at least one sensor (6; 7) arranged upstream of said linear camera in the advancing direction of said movable supporting surface; - detecting a "trigger event" signal, generated on the basis of said presence signal, said linear camera starting to acquire an image of said object on the basis of said "trigger event" signal; - starting to acquire an image of said object by said linear camera, when said object has travelled a preset distance from said preset position, said distance depending on said at least one dimension of said object and/or on the position of said object on said movable supporting surface, said distance being calculated by an advance sensor associated with said movable supporting surface, said advance sensor being suitable for generating a signal comprising an electric pulse at each preset movement of said movable supporting surface, said advance sensor being operationally connected to said linear camera, or to a control device that controls said linear camera, characterised in that it further comprises: - setting a mode for image acquisition of said linear camera on the basis of the resolution of said advance sensor, said setting comprising selecting said acquisition mode from a plurality of different acquisition modes, said resolution consisting of a distance travelled by said movable supporting surface in the time that elapses between two successive pulses generated by said advance sensor.