Low-cost physically unclonable functions (PUFs) can be deployed with consumer products to deter counterfeiting. An intrinsic physical property - unique textures of paper or other surface - has received strong interest. Extrinsically introduced features, such as randomly positioned bubbles and fiber segments, have also been deployed in the industry to facilitate authentication. This paper carries out a study to gain a better understanding in the factors affecting the authentication performance, with a consideration of the friendliness under mobile imaging. Comparisons are made for paper-based PUFs of different characteristics. It is found that the density of foreground objects have a dominant impact on the authentication performance.