Let's assume you public space has only floor and back wall and let's try to think how the photo was shot and how the photographing could be modelled. Here's my sketch for the scene:

[![enter image description here][1]][1]

The red spot C is my camera. It constructs a perspective image. To get an equivalent, but bigger size image than the sensor of my camera I put my imaging plane P in front of the visible part of the floor. A and B are those parts of the floor and back wall which are cropped out of the photo.

If there's something on the floor you can get the right view of it by placing a smaller size version of the same 3D object in front of the Image plane:

[![enter image description here][2]][2]

That's because the same sight lines fit.

Let's assume you place a flat photo in the place of the imaging plane P in a 3D program. It replaces the public space. I guess it's very difficult if you have no measurements made in the public space. If you know some measures you can construct something like my floor and back wall to find the proper place for the camera (=crossing of the sight lines).

The focal length must also be adjusted. It affects scaling and how wide the view can be. I skip all calculations for it.

If you succeed to find the right place for the camera and the flat photo you can place 3D objects between the camera and the Image. As you obviously hope they will look geometrically right.

But you cannot put anything partially behind the objects that exists only in the photo. In addition no light interactions happen. You cannot for ex. place anything into a shadow which is in the photo.

If your intention is to create a visualization how some still non-existent objects would be placed into the public place the result can still be useful. You can render the 3D scene without the Photo. You put it back in Photoshop as a background layer and wipe off the those parts of the rendered 3D objects which are covered by things in the photo. With hard work you can even create plausible shadows and adjust colors to somehow compatible.

But do not expect photorealistic results. SketchUP alone creates only renderings which more or less resemble drawings. 

SketcUP has light adjustments so you have chances to get the shadings of the objects to match with the general direction of the light in the photo.

I must admit I don't have current version of SketchUP because it doesn't run in my museum grade computer ==> I cannot write an exact "how to do" receipe.

  [1]: https://i.sstatic.net/j5ffi.jpg
  [2]: https://i.sstatic.net/6PZAc.jpg