Trick Photoshop

I will be creating an effect of an image behind a glass. By this I mean I will make the girl appear inside the glass jar. If you use Blend Modes such as Overlay or Soft Light or Screen or whatever here you may not get the exact effect you want. So let me try something different.

I will be using this free stock image. It belongs to *LunaNYXstock Elisabeth

or the Magnetic Lasso, whichever you prefer to use. (Click the hightlighted words to go to the relevant tutorials.)
Step 2 : I have cut out the girl's image.
 Step 3 : I have cut out the jug image.
Step 4 : Click off the eye icon in the Background layer of the girl's image.
Step 5 : Click off the eye icon in the Back ground layer of the jug.
 The jug image  looks like this.
 The girl's image looks like this.
 Step 6 : Click on the girl's image. Press CTRL+A (Select All). Then press CTRL+C (Copy).
 Step 7 : Click on the jug image and press CTRL+V (Paste). The girl's image is pasted onto the jug.
The resolution of the girl's image is low compared to the jug. Therefore the girl's image is small. We will fix that.
Step 8 : The Layers palette looks like this. Layer 2 is the image of the girl and Layer 1 the jug. The Background layer is switched off.
Step 9 : Click on Layer 1.
Step 10 : With Layer 1 highlighted, press CTRL and click the New Layer icon. A new Layer 3 forms under Layer 1.
Step 11 : The Foreground/Background Colors should be set to the default Black/White respectively. 
If not press x and then d on the keyboard.
Step 12 : Press CTRL+BACKSPACE. This will fill with the Background Color which in this case is White.
 This is how the image looks with the background filled with White.
 Step 13 : Click on Layer 2. This contains the image of the girl.
Step 14 : You can also rename the layers. Double click where the small white hand points to and you can then type in a name. 
Click once after typing. I have renamed the layers  'girl' and 'jug'. 
Step 15 : Click on the Girl Layer.
 Step 16 : Press CTRL+T. A selection forms around the image of the girl.
 Step 17 : After pressing CTRL+T. Press SHIFT+ALT and you will be able to resize the image of the girl
proportionately.
 Step 18 : Once you are satisfied, press ENTER to apply the selection.
Step 19 : Click on the jug layer. Press ALT and drag up. A copy of the jug layer will be placed on top of the girl layer.

 This is how the image looks. The girl's image is hidden.
Step 20 : Click on the girl layer.
 Step 21 : Click on the New Fill or Adjustment Layer button. Click Brightness/Contrast from the pop up. 
A Brightness/Contrast Adjustment Layer will form.
Step 22 : Click on the jug copy layer.
Step 23 : Press CTRL+ALT+G. This creates a Clipping Layer. 
You will find a small bent arrow beside the layer thumbnail on the jug copy layer. 
Step 24 : Ctrl+Click the layer thumbnail on the jug copy layer.
 Step 25 : A selection of marching ants surround the jug. Press CTRL+C (Copy).
Step 26 : Press ALT and click directly on the Mask of the Brightness/Contrast layer. 
 The image looks like this.
Step 27 : Press CTRL+V. The selection made in Step 25 is pasted into the Mask.
 The image looks like this. It is in black and white.
Step 28 : Click on the jug copy layer.
 As soon as you click the jug copy layer, the girl becomes visible behind the glass. Press CTRL+D to deselect. 
 Step 29 : Lower the Opacity of the Jug copy layer to 75%.

This is how the image looks.
Step 30 : Click on the Girl Layer.
Step 31 : Press ALT and drag the girl layer to the top. It will form a duplicate girl copy layer.
Step 32 : Lower the Opacity of the girl copy layer suitably. It will depend on your image.
I have lowered it to 55%.

The image looks like this.
Step 33 : Click the New Fill or Adjustment layer button. Click on Levels.
Step 34 : In the Levels dialogue box drag the Gray Slider in the middle slightly towards the left. This of course will also depend on the image you use.
Here is my finished image.
Other photoshop tutorials are here