The surfaces to be modeled by dense point clouds need to have a visible random texture/pattern. Examples of random textures are rock, dirt, skin, wood grain, bricks, trees, etc. Examples of surfaces that are not textured are plaster-board walls, metal surfaces or glass windows. Some items may appear to be textured but the texture is consistently repeated and not random (certain cloth patterns, man-made objects like a window screen, or a faux-leather pattern).
A surface with no texture (a body panel of a car for example) can still be DSM modeled if a random texture pattern is applied or projected onto it. A random dot pattern (PhotoModeler Technologies Support can provide a file) put on a 35mm slide or a gobo slide and projected on the surface can give enough texture to extract the surface in 3D. It is important to ensure that the surface and projector are not moving during the photography.