At first: The shadow of an inserted object cannot be realistic before the object itself and its interaction with the background are generally realistic (or at least seem to be).
The effect of a bottle, which is made of bright uncolored glass, has several parts
Reflected lights as highlights
Reflected environment (=distorted images with reduced opacity)
Refracted (seen through glass) lights as another type of highlights, bright lights can be well visible from nonpredictable directions, because they can walk inside the glass nearly around the bottle without becoming unnoticeably dim
Refracted environment, distorted like seen through a bizarre lens
Glass itself is a little hazy, but its opacity is very low
A shadow is generated because the glass reflects and refracts the light off and also absorbs a little.
Intensified lights somewhere in the environment, interleaved with the shadow, caused by the lens effect and reflection of the glass
On soft platform the bottle makes a dimple due the weight or placing impact
Quite complex, I say! I have seen software (Blender and its commercial multi 1000$ counterparts) which handle this all with 3D and physics modelling, but it's far beyond my skill level and the scope of this answer. In the next example we do only few of them and we rely on fake methods with 2D images.
I have noticed that a photo of a bottle must be adapted to the background. It cannot be made nicely transparent, reflecting, shadow making and background refracting without the final environment photo. (A guru probably could construct a smart enough filter which needs only a new environment image and few slider adjustment to fit perfectly again. We skip it)
Let's start. Have a bottle photo - background already removed, desaturated, fully opaque, but with no adaptation attempts still done. Add it as a layer onto your background image (layer name = Landscape):
Make a copy of the bottle with exaggerated edges. Use Filters > Stylize > Find Edges. Let it have Blending mode = Multiply to remove white. Here it's shifted temporarily a little apart
The bottle can be made transparent with blending mode Hard light. Over 50% brightness areas lighten the background, darker than 50% makes the background darker. A curves layer with "only the next layer"-switch is needed to adjust the effect. Obviously you don't want too much white and definitely not too much darkness
The Edges-only version with reduced opacity adds definition. Insert the original bottle with very low opacity (=normal blending) on the top. They together with the hard light layer are quite plausible bottle:
You need a shadow. Make a copy with the hard light layer + its adjustment layer. With different (darker) adjustment, moving it downwards, distorting (= Edit > Transform > Distort) and blurring (= Filters > Blur > Gaussian Blur) little it can be plausible shadow. Blur describes that the light is not fully from one point. It's also an aid. Blur reduces the need of warp the shadow along the bumps of the underlying background, which is skipped here:
Note that the max brightness of the shadow curve is 50% (=no effect). You cannot get good intensified light areas by having brighter curve. It needs curve adjustment to the background and the bottle must be in the layer mask. That's also skipped here => We have no intensified light spots on the background.
As mentioned, the bottle distorts the through seen background including the shadow. We make a merged copy, where the shadow is applied to the background and distort it with liquify.
Duplicate the background image layer and the shadow with its adjustment layer. Merge at first the shadow and its adj layer, then merge the result with the background.
Duplicate the result. You need it as a spare and also otherwise later. Shut the original shadow- and background layers, but do not remove them.
Make a selection which covers the bottle You can Select the emptiness around the bottle with the Magic Wand and invert the selection. Then goto the merged shadow+background layer and start Filters > Liquify:
There is applied Bloat in the middle, Puck at the edges and the bottle is walked around to make it clearly different. This is fully fake distortion, but makes the existence of distortion obvious. Probably you must try several versions until a good one is found. The result:
There's also applied the following tricks:
- The adjustment curve of the hard light layer is made a little concave. That contrast boost makes the distortion better visible without reducing the brightest highlights.
- The distorted merged layer is made partially transparent, it reduces the artificiality of the distortion because something original also exists
- a few spots in the distorted layer are erased because they seemed disturbingly artificial.
NOTE The bottle is placed onto the background without any digging nor other soil moving works. If you need them, you must do them in the beginning. The shadow is more defined than if the sky were fully cloudy. So a little sun glittering would be an useful addition. Here two pieces of glitter is added (Beware, this transforms easily your image to a cartoon):