1. A method comprising: obtaining a specific image; calculating an edge characteristic value of multiple pixels of the specific image; finding a pixel whose edge characteristic value is a local maximum value along a slope direction of the pixel; when the edge characteristic value of the found pixel is larger than a preset characteristic value threshold, filling the pixel whose edge characteristic value is the local maximum value with a preset color; scanning the specific image; counting an amount of pixels whose color is the preset color at a scanning line of the specific image; and when the amount of pixels whose color is the preset color is larger than a preset number threshold, determining a line where the scanning line locates as an edge line of a frame of the specific image.