To obtain a photorealistic rendering of your BikeCAD model, first export the model to FreeCAD. Import the resulting Python script into FreeCAD and click the green execute button to obtain a 3D model of your design. In this example we'll generate our photorealistic image using the ray tracing program CADRays by OpenCascade. To prepare for this, we'll need to export our model as a collection of STEP files. On the left side of the FreeCAD interface, we'll see the Tree View which lists each of the elements that make up our design. We'll hold down the ctrl key and select all of the elements representing the frame of the bike. That will include the left and right dropouts and all the tubes. We'll select File >> Export and export all these items as a single STEP file. We'll repeat this process for bolts and the derailleur hanger, the seatpost clamp and again for the various logos that will appear on our frame.
We'll then open CADRays and select File >> Import and read in each of the STEP files exported from FreeCAD. We'll define the up direction in the model space as being the Y coordinate.
Looking at the models brought into CADRays, we can see that they've each defaulted to a shiny gold colour. We can go through each of these models and assign a unique material type and colour. You'll probably want to experiment with different materials. In this example, we'll select metal for the frame and right click on the color square to select a shade of green. For the derailleur hanger and bolts, I'll also choose metal, but I'll assign a gray colour. I'll choose a glossy black for the seatpost clamp and matte white for the logos.
The resulting image can be saved using File >> Save image.