“…Preprocessing mainly includes gray histogram enhancement [4], signature extraction [5], edge information enhancement [6], and image size normalization [7]. Feature extraction includes gradient [8], SIFT [9], posetoriented grid features [10], entropy [11], biological features [12], HOG features [13], histogram [14], LBP [15], and wavelet [16]. Signature authentication mainly includes SVM [17], KNN [18], neural network [19], deep learning [20], hidden Markov model [21], and artificial immune system [22].…”