2.5D effects like occlusion and surrounding, which incorporate 3D blending in 2D designs, enhance visual dynamics and realism. However, it is hard to create 2.5D effects due to complexity of human depth perception and the labor intensive task of realistically conforming design elements to real-world perspective and occlusion. We introduce DepthScape, a Human-AI collaborative authoring pipeline that creates 2.5D visual designs by placing design elements in an estimated depth space. Leveraging a single-view 3D reconstruction model, DepthScape processes input images into 3D scenes, enabling realistic 2.5D effects by positioning and rendering visual elements in the 3D scene. DepthScape also suggests element placement in the 3D space based on examples from our design library, and provides interface for users to further fine tune the design