Typically you would use Photoshop for this type of compositing. You cannot do anything like this in Lightroom. This is an advance tutorial so the different tools will not be explained such as understanding selection, the brush tool, masking or the adjustment layers.

The first step would be placing. For a composite to work we need consistency in perspective and lighting. That means that both images were taken with the same camera, with the same focal length, with an identical camera angle.  And then we have consistency in lighting. You can see that I created or placed a small point-shaped source in the right spot.

I have covered the worktop with a gray piece of cardboard that mimics the visual quality of the tarmac. I placed a yellow or a beige coloured piece of cardboard behind the flower to create highlights like these ones here. OK, so the first one would be placing I use the move to, to move the flower image onto the so-called backdrop. And strictly speaking, we don’t need this flower image anymore. I’m going to minimise it and put it into the dock.

I would decrease the opacity to 50 percent. So I make the top layer semi-transparent. And that’s going to help me place it, putting it just in the right spot. We’ve got a good reference point here of the light. So I’m going to place it right on top of each other like this. That’s looking good. So I’m going to increase the opacity again to 100 percent. 

The second step would be to mask the background.

So for this to work, we need to select the background first, and we start by adding a layer mask to the object layer.

 I personally like to use selection tools. We’ve got three selection tools that would be suitable here. 

The first one would be the polygonal lasso tool, if you would like to do the work manually.

The second one would be the so-called magnetic lasso tool that traces edges. 

And the third one is the so-called magic wand, too. That’s the one I’m going to start with. The magic wand works by selecting similar pixels. That is what you control with sort of the so-called tolerance. So our aim is going to be to work with a small tolerance and then to add to the existing selection. So I’m going to select a tolerance of 10. And then I’m going to click on the background, you can see that those pixels are very similar.

They’re similar enough to end up in the same selection. And those pixels here are already too different. So I guess they’re a little bit too light to be part of the same selection. And here comes the trick from the top left hand corner, I select the so-called “add to” selection function. And now when you look closely at the curves, you can see a little plus next to it. That means every new selection that I’m going to do is going to be added to the current selection.

So when I click here, then I can extend the selection bit by bit.

And now I go all the way around the flower. I am going to select just little gaps in between. Don’t worry, if this selection is not perfect, you’re going to tidy up the edges later on. Particularly like you of the entire background, because they just became too different to become to be part of the same selection. But ultimately, this is something that I have to do with a different selection tool.

I can see it some one point it tends to spill over. And I’m going to use the polygonal lasso tool here again. I’m going to select the “add to” selection function. OK, that’s looking better. I still need to refine a few edges here, particularly down here. That’s looking good. I need to get rid of the background and we do this by filling it with black into the mask. But before we do this, if you zoom in very closely here, can you see that the magic wand tool has left a very, very fine, light edge just around all those details.

And I can address this by expanding the selection. I do this by going to select, then modify and then expand. And I’m going to expand it by about two pixels. That should do. Can you see now the selection has expanded, so that’s doing just what I want and then I’m going to fill the zoom out, then I’m gonna fill the selection with Black into the mask. So make sure that you have selected the mask channel, and then I’m going to fill it by going to edit and then fill and then with black.

Tthe background now disappears. Remember, we have not deleted anything. We just filled it with black and remember black hides and white reveals.  We need to refine the edges a little bit because they are completely sharp. Can you see this doesn’t look quite realistic. And I can address this problem by, again, by selecting the mask itself and then I can slightly feather the edges.

This one here would be too much. I’m going to opt for about one pixel.  I think that’s looking pretty realistic. Then third step would be to grade the object to match the background. And we do this by placing a curve’s adjustment layer right on top of the object layer. And then we’re going to link these two by holding down the alt key. And then you click right in between. Can you see? Whatever you change, if you apply to the curves layer applies only just to the object layer underneath.

I can use this to alter and to adjust the look and feel of the object layer to match the background. That’s looking good. I think it needs to be a tiny bit lighter. Good. And the fourth step would be to apply the shadow. Now, we do this by creating a curve’s adjustment layer in between the background layer and then the object layer. And then we pull down the WidePoint to mimic the visual qualities of a shadow.

Curves layer, and then we’re going to pull this down to about this type of value here. Now, we don’t want this to apply to the entire image. And because of this, we need to, again, fill the mask with black.

Edit fill with black. Just like this, and now we’re going to use the brush tool and we’re going to use an opacity and a flow of about 30 30. Make sure that you use white as the foreground colour because you want to gradually reveal the properties of this shadow layer in between. And now you can brush this in. You can see that I slightly went a little bit too far here, and I can remove this effect or the shadow by using black as the foreground colour.

 And now as a next step, I think we need an additional shadow on the vase itself. And that’s something that I need to apply to just to the vase layer. So I’m going to create another clipping adjustment layer on top of it. curves.  I am going to make this darker.  I’m going to fill the mask with black. And now, again, white as the foreground colour and brush in.

 And the last step would be the final grading. So I’m going to apply two curves adjustment layers on top of all the different layers. The first one is going to control the brightness. 

The one on top of it is going to control the contrast. And I am going to create one for new saturation. So to control the brightness.I just need to apply one anchor point pretty much in the middle.

The second one would control the contrast which I’m going to increase slightly. And then here  saturation allows me to control the intensity of the colours.  I just need to balance the final results,. Now, looking at it, the shadow is a little bit too intense.

 And I can then control the brightness, the contrast of the flowers itself. It’s going to look a bit more like this. Shadow on the vase itself. OK. I just found that I need a bit more density right here. I am going to create another curve’s adjustment layer on top and I’m going to fill with black. And I’m going to use the brush tool again with white.

Just a little bit more density around here.