A method of producing a multiplicity of quality indicators including a changeable barcode, said quality indicators being operative to provide a machine-readable indication of exceedance of at least one product quality threshold by at least one product quality affecting parameter, the method comprising: printing a background using a first material having at least one selectable visually-sensible characteristic which is invariable with respect to said at least one product quality affecting parameter; and printing a changeable barcode using a second material having at least one variable visually-sensible characteristic which gradually changes as a function of changes in said at least one product quality affecting parameter, said machine-readable indication of exceedance of said at least one product quality threshold being represented by a machine-readable difference between said at least one selectable visually-sensible characteristic and said at least one variable visually-sensible characteristic, characterized by: receiving non indicator-specific inputs including characteristics of a first plurality of materials each having at least one selectable visually-sensible characteristic which is invariable with respect to a plurality of product quality affecting parameters; receiving non indicator-specific inputs including characteristics of a second plurality of materials each having at least one variable visually-sensible characteristic which gradually changes as a function of changes in said plurality of product quality affecting parameters; receiving an indicator-specific input including a set of thresholds of product quality affecting parameters whose exceedance is to be indicated by said multiplicity of barcoded quality indicators; and selecting said first material based on said characteristics thereof for printing said background and said second material based on said characteristics thereof for printing said changeable barcode in order to provide said machine-readable indication of exceedance of said at least one product quality threshold by said at least one product quality affecting parameter. printing a background using a first material having at least one selectable visually-sensible characteristic which is invariable with respect to said at least one product quality affecting parameter; and printing a changeable barcode using a second material having at least one variable visually-sensible characteristic which gradually changes as a function of changes in said at least one product quality affecting parameter, said machine-readable indication of exceedance of said at least one product quality threshold being represented by a machine-readable difference between said at least one selectable visually-sensible characteristic and said at least one variable visually-sensible characteristic, characterized by: receiving non indicator-specific inputs including characteristics of a first plurality of materials each having at least one selectable visually-sensible characteristic which is invariable with respect to a plurality of product quality affecting parameters; receiving non indicator-specific inputs including characteristics of a second plurality of materials each having at least one variable visually-sensible characteristic which gradually changes as a function of changes in said plurality of product quality affecting parameters; receiving an indicator-specific input including a set of thresholds of product quality affecting parameters whose exceedance is to be indicated by said multiplicity of barcoded quality indicators; and selecting said first material based on said characteristics thereof for printing said background and said second material based on said characteristics thereof for printing said changeable barcode in order to provide said machine-readable indication of exceedance of said at least one product quality threshold by said at least one product quality affecting parameter. receiving non indicator-specific inputs including characteristics of a first plurality of materials each having at least one selectable visually-sensible characteristic which is invariable with respect to a plurality of product quality affecting parameters; receiving non indicator-specific inputs including characteristics of a second plurality of materials each having at least one variable visually-sensible characteristic which gradually changes as a function of changes in said plurality of product quality affecting parameters; receiving an indicator-specific input including a set of thresholds of product quality affecting parameters whose exceedance is to be indicated by said multiplicity of barcoded quality indicators; and selecting said first material based on said characteristics thereof for printing said background and said second material based on said characteristics thereof for printing said changeable barcode in order to provide said machine-readable indication of exceedance of said at least one product quality threshold by said at least one product quality affecting parameter.