Putting a photo on a building wall with the correct perspective.

I am going to throw in another idea, since someone has woken this old thread. An idea I think way more fast and simple than some other ideas in the thread.

We have the tractor cutout and the building.

We make the tractor layer a Smart Object so that a) we keep the handles in their original corner locations, and b) because it is central to making this method work. 

Note: I copied the foreground grass to a new layer at the top of the stack, so bottom of the tractor can be placed behind it.

The OP did not say how large the image should appear on the building, so I am going assume about 70% of the height of the building.

Double click the Smart Object to open in a new window so we can edit it, and add Relative 30% to the height of the canvas.

The bounding box will now surround an area relative to the full height of the building, and we can Ctrl/Cmd drag the corner handles into place keeping perspective close to spot on.

We can improve this in a couple of ways. 1) If you have Windows and Lazy Nezumi Pro, you can use its Vanishing lines preset to draw some accurate perspective lines as a guide.  Note: I have a Curves layer which I have turned off in this screen shot.  This was to temporarily increase contrast between the blocks and concrete pointing so I could more accurately position the lower Vanashing Line.

We can now get the perspective spot on when placing the tractor, and turn off the guide lines.

If you don't have Lazy Nezumi Pro, then a) I am sad for you, and b) use the grid graphic that we should all have in a CC Library.  Open the SO to edit, and place your grid layer at the top of the stack.  Use that to place the tractor on the wall. Open the SO to edit again, and turn off the grid layer.

You’re getting some good options because there’s more than one way to do this, you just have to pick one.

Here is a quick demo of another way to get a first draft done in about a minute. You just need three layers and a mask, and it’s adjustable.

Notes:

• Dragging the Quick Selection tool over the wall rapidly isolates a selection of it. 
• Adding a Solid Color Fill layer automatically creates a mask of that selection, so that your “wall paint” color affects only the wall, not the entire scene. 
• Because the wall paint is a Solid Color Fill layer, you can change its color at any time by double-clicking it, as is done frequently during the demo. 
• After the farmer photo is added as a layer with drag-and-drop, Edit > Free Transform is used to fit it to the wall. The perspective distortion is done by dragging a Free Transform corner handle while holding down the Command key (Mac) or Ctrl key (Windows). [CORRECTION: You can also do this more simply, without remembering any keyboard shortcuts, by choosing Edit > Transform > Perspective. The way I did it was a more advanced way, using the key press to modify how Free Transform works.]
• The Solid Color Fill layer and farmer photo layer are blended with the wall (letting the wall texture show through) using the blending mode menu and Opacity value in the Layers panel; adjust these until they represent the mural visualization you want. 

The animation quality is a little low because I had to compress it a lot to get it under the 10MB limit for an inline graphic in a post.

Open the picture and add a blank layer. Use filter-Vanishing Point to make a grid of the wall. Click the bar symbol (upper left corner) and from the dropdown choose Export Grids to Photohop. Paste your mural on a layer above the grid and use distort to match the grid lines.

What projector will you be using?  How much 'keystone' correction does it have?  My projector does not have any keystone correction because it uses lens off-set like a technical camera, so if I am understanding you correctly, that sort of projector would not work for you.

So it might come down to producing a test image like below and projecting that on the building wall to see how it fits, and if you can correct any keystone error, and then using that as a guide to setting up your images.

A lot depends on the height of the projector of course.  If it is located half the height of the wall and perpendicular to the wall's centre point, then it will not need any correction.  Without being 100% clear on your objectives, we can only guess at how best to achieve them.

@harleypublisher So this is a one minute example I made just to find out if this is what you are after or do you want something else altogether?