1. A handheld electronic device, comprising: a camera module, configured to take pictures; a flashlight module, configured to generate at least a first light having a first spectrum and a second light having a second spectrum; and a processor, configured to: generate a flashlight indication signal having one or more pulse(s) distributed over time; direct the flashlight module to turn on the first light and the second light at different time based on the flashlight indication signal; direct the camera module to take pictures to obtain a stream of biological characteristic images comprising one or more first biological characteristic image(s) obtained when the first light is turned on and one or more second biological characteristic image(s) obtained when the second light is turned on; and compare the first biological characteristic image(s) with a first reference signature and compare the second biological characteristic image(s) with a second reference signature to obtain an identity authentication result.