1. An image acquiring method comprising: acquiring a first image; determining a first sub-image corresponding to a first object from the first image; and replacing the first sub-image with a second sub-image different from the first sub-image to obtain a second image, wherein the determining the first sub-image corresponding to the first object from the first image comprises: analyzing a first area of the first image; and determining a sub-image complying with a predetermined condition as the first sub-image, wherein the analyzing the first area of the first image and the determining the sub-image comprise: dividing an image corresponding to the first area into M sub-images, M being a positive integer; performing a color channel histogram analysis on each of the M sub-images to determine M color histograms; determining a first color histogram from the M color histograms, an absolute value of a difference between the first color histogram and a second color histogram of a neighbouring area being larger than a first preset threshold; and determining a sub-image of an area, to which the first color histogram is related, as the first sub-image.