You can do this inside Mecabricks with a custom background. In the 3D Rendering workspace, look for the Background tab. It's the third tab in the middle grouping on the right hand side bar. Change the Type from Colour to Image. Now you can upload an image using the piece of paper icon. Alternatively, you can render your image in Mecabricks without the background and then use an image editor like Photoshop or Gimp to composite one in.

Of course, you can also export your project to a full 3D program like Blender. In there, you have much more control over every little aspect of a render, but it takes a bit more of a learning curve in some ways over the Mecabricks renderer. If you can post examples, maybe someone here can help you with how to get that look.

Cheers!

Thanks!