1. An image processing device comprising: a processor; and a memory which stores a plurality of instructions, which when executed by the processor, cause the processor to execute: determining whether or not an eye region of a user being detected a line-of-sight in an image resulting from photographing an eye of the user is influenced by reflection light, the eye region being a region of the eye; acquiring first feature values of a first combination of pixels included in the eye region when it is determined that the eye region is influenced by the reflection light; and detecting, as a feature portion of the eye that is used for detecting a line-of-sight of the eye, a region that includes one pixel of the first combination when second feature values of a second combination of pixels that is the same as or similar to the first feature values are included in features being accumulated for respective strengths of influences of the reflection light that appear in images of the feature portion of the eye.