A collage is an artistic composition made by assembling different parts to create a new whole. This procedure can be applied for assembling tridimensional objects. In this paper we present CollARt, a Mobile Augmented Reality application which permits to create 3D photo collages. Virtual pieces are textured with pictures taken with the camera and can be blended with real objects. A preliminary user study (N=12) revealed that participants were able to create interesting works of art. The evaluation also suggested that the possibility of itinerantly mixing virtual pieces with the real world increases creativity.