The section newmtl in the mtl file can contain a line starting with "map_Kd " followed by a path and file name to a texture image file. Usually there is no path and just a filename which indicate the texture images should be in the same folder as the obj and mtl file.
Possible cause for not seeing a texture: the referenced texture image doesn't exist, is named differently, has an invalid image format, or has a wrong path.