Example of difference images of two epochs of the FRB190102 field, where one of them includes a mock point-like source injected with different magnitudes: a non-detected source (S/N < 3; left panel), a limiting magnitude (S/N = 3; center panel), and a well-detected source (S/N > 3; right panel). The pale yellow circle indicates the position where we injected the mock star with an aperture radius of the size of 1 FWHM as reference.