Weld lines are caused by the convergence of two separate flows of molten plastic and are found on most plastic injection-molded parts. Although weld lines are often unavoidable, it is possible to minimize their cosmetic effects through careful product design and manufacturing process control. In this study, visual differences in the area adjacent to a weld line were investigated as part of an analysis of the surface quality of molded parts. A flat sample injection mold (90 mm × 54 mm × 3 mm) with a square hole (30 mm × 20 mm) was developed. A core could be inserted into the mold from different directions to create dynamic and static welding lines. The mold surface was textured to create observable differences in texture structure around the welding line when acrylonitrile butadiene styrene was used as the molding medium. The injection molding parameters, holding pressure, mold temperature, and injection speed were considered in analysis of visual differences in the welding lines. Welding line structure was observed using a laser scanning microscope. A digital single-lens reflex camera, rather than unaided human vision, was employed to observe the image from various angles. The experimental results were compared with results obtained using the Moldex3D software. The filling ratio of the textured structure was the major factor affecting the visual appearance of the welding line. The visual appearance can be improved by reducing the skin layer thickness and pressure difference by using a higher injection speed, holding pressure, and mold temperature.