1. An image capturing method with supplemental lighting modulation, applied to a monitoring apparatus having a lighting unit and an image detecting unit, the image capturing method comprising: dividing a working period of the lighting unit into at least one first sub-period and at least one second sub-period; driving the lighting unit to respectively emit supplemental light with different intensity during the first sub-period and the second sub-period; driving the image detecting unit to respectively capture a set of monitoring images with a predetermined amount during the first sub-period and the second sub-period; comparing the monitoring image captured in the first sub-period with ones captured in the second sub-period; and analyzing definition of the set of monitoring images and selecting one of the monitoring images having the definition greater than a threshold to execute image recognition.