A method of image processing comprising: obtaining by an imaging device a low resolution version and a high resolution version of a retail image, wherein the retail image is an image acquired in a retail store of a retail unit, the high resolution version of the retail image being a temporary file to be erased automatically after a predetermined time period; transmitting the low resolution version of the retail image to a server comprising an item database associating identified items with visual signatures distinguishing said items; carrying out a recognition process on the low resolution version of the retail image using a recognition server, by searching the low resolution version of the retail image for visual signatures associated with identified items by the item database; detecting (S 140) an unidentified item in the low resolution version of the retail image with a visual signature which does not match any of the visual signatures associated with identified items by the item database; cropping the low resolution version of the retail image by the server to form a basic item image around a contour of the unidentified item; storing the basic item image in the item database; and updating the visual signatures corresponding to identified items in the item database by storing in the item database the visual signature associated with the basic item image; upon receipt of a request from the server, (S 150) the request including data representative of the contour of the unidentified item in the low resolution version of the retail image, cropping a high resolution item image from the high resolution version of the retail image (S 160), the high resolution item image corresponding to the contour of the unidentified item; transmitting (S 170) the high resolution item image to the server; and updating (S 180) the item database with the high resolution item image, wherein the basic item image is replaced by the high resolution item image in the item database after the high resolution item image is transmitted by the imaging device. obtaining by an imaging device a low resolution version and a high resolution version of a retail image, wherein the retail image is an image acquired in a retail store of a retail unit, the high resolution version of the retail image being a temporary file to be erased automatically after a predetermined time period; transmitting the low resolution version of the retail image to a server comprising an item database associating identified items with visual signatures distinguishing said items; carrying out a recognition process on the low resolution version of the retail image using a recognition server, by searching the low resolution version of the retail image for visual signatures associated with identified items by the item database; detecting (S 140) an unidentified item in the low resolution version of the retail image with a visual signature which does not match any of the visual signatures associated with identified items by the item database; cropping the low resolution version of the retail image by the server to form a basic item image around a contour of the unidentified item; storing the basic item image in the item database; and updating the visual signatures corresponding to identified items in the item database by storing in the item database the visual signature associated with the basic item image; upon receipt of a request from the server, (S 150) the request including data representative of the contour of the unidentified item in the low resolution version of the retail image, cropping a high resolution item image from the high resolution version of the retail image (S 160), the high resolution item image corresponding to the contour of the unidentified item; transmitting (S 170) the high resolution item image to the server; and updating (S 180) the item database with the high resolution item image, wherein the basic item image is replaced by the high resolution item image in the item database after the high resolution item image is transmitted by the imaging device.