Photomontage is the process (and result) of making a composite photograph by cutting and joining a number of other photographs. (from Wikipedia)
Some contemporary artists who use photomontage:
Jerry Uelsmann Robert and Shana Parke Harrison Loretta Lux Maggie Taylor
Using Layer Masks (from Adobe Photoshop Help):
You can add a mask to a layer and use the mask to hide portions of the layer and reveal the layers below. Masking layers is a valuable compositing technique for combining multiple photos into a single image or for making local color and tonal corrections. 1. In the Layers palette, select the layer.
2. Do one of the following:
To create a mask that reveals the entire layer, choose Layer > Layer Mask > Reveal All.
To create a mask that hides the entire layer, choose Layer > Layer Mask > Hide All.
3. Click the layer mask thumbnail in the Layers palette to make it active. A border appears around the mask thumbnail
4. Select any of the editing or painting tools.
Note: The foreground and background colors assume default grayscale values when the mask is active.
5. Do one of the following:
To subtract from the mask and reveal the layer, paint the mask with white.
To make the layer partially visible, paint the mask with gray. Darker grays make the level more transparent, lighter grays make it more opaque.
To add to the mask and hide the layer or group, paint the mask with black. The layers below become visible.
To edit the layer instead of the layer mask, select it by clicking its thumbnail in the Layers palette. A border appears around the layer thumbnail.
Working methods to create photomontages:
Note: these methods are suggestions based on my own preferences. There are many ways to accomplish the same effects with different tools or strategies in Photoshop. I have used menu bar commands rather than shortcuts in these instructions. Things to consider when choosing photos for a photomontage
Is the direction of light consistent? Flipping the photo is sometimes all that you will need to do ( Edit > Transform > Flip Horizontal will flip the layer or Image > Rotate Canvas > Flip Canvas Horizontal will flip the entire image). Are photos at the approximate relative sizes that they need to be in the montage?
To check relative sizes of your photos, zoom all photos to the same magnification ( View > Zoom In or Zoom Out). You will see that percentage of magnification on the top bar of each photo’s window. If there is a great difference in size, it is best to resample the image before adding it to the montage (Image > Image Size). Smaller size differences can be handled within the montage by using Edit > Transform > Scale.
*** When resizing with Transform, HOLD THE SHIFT KEY while dragging a CORNER HANDLE to maintain correct proportions**
Is color consistent?
Color corrections can be done to appropriate layers after montaging. One method to try: Image > Adjust > Color Balance
Using Layer Masks – “White Reveals, Black Conceals”
Any painting tool (Brush, Pencil, Paint Bucket, Gradient) may be used in the mask. **make sure that the mask (and not the image in the layer) is active by clicking on the mask icon in the Layers Palette. Otherwise, you may find yourself painting on your image. To activate the image, click on its icon in the Layers Palette.**
I like to create a white layer ( Layer > New > Layer ) that I can drag under layers that I am working on when I need to isolate that layer to see what I am doing. This layer can be deleted later.
Using a Brush
I find that I get the best results when using a soft brush (around 80% Hardness) at low opacity (10%-12%) at the largest size that is practical for the situation. This will reduce the visibility of hard edges and overlapping strokes. To change brush attributes, click on the Brush tool and use the menu bar at the top of the screen.
Using the Gradient Tool
Choose White or Black (depending on whether you are revealing or concealing) as your foreground color in the Tool Bar. Click on the Gradient tool. At the top of the screen you will see a menu bar with your gradient options. Make any necessary changes. To apply a gradient to the mask, click on the mask icon to activate it. Then, click in the image window at the point you want the gradient to begin, then drag to the point that you want the gradient to end and release mouse button. To constrain the angle of the gradient to horizontal, vertical or 45 degrees, hold the Shift key down as you click and drag.
Straightening a tilted image
Use the Ruler Tool (found on the tool bar by clicking on the Eyedropper Tool and keeping the mouse button down so that the menu of other tools pops out. Choose the Ruler Tool from this menu). Establish a correct vertical or horizontal line by clicking and dragging the Ruler Tool. Next, rotate the image ( Image > Rotate Canvas > Arbitrary ) You will see a degree of rotation has already been entered in the dialog box. Click OK.
Controlling the Crop Tool
When using the Crop Tool to make slight crops, the tool will seem to have a mind of its own and snap to what it thinks the edge should be. To override this, hold down the Control key while using the Crop Tool.
Soften selection edges
When placing an image into a montage, a hard edge on the pasted image can emphasize that it was added in to the picture. A softer edge can reduce this effect. If you use selection tools to cut out an object to place into your montage, here is one way to slightly soften the edges:
Objects or people in environments usually cast a shadow. Adding shadows can help unify a photomontage. This is a basic method to create a cast shadow:
Make a selection of the object that will be casting a shadow. A white layer placed under this layer can help isolate the object and make selecting easier.
Make a new layer ( Layer > New > Layer ) and fill this selection with black using the painting tool of your choice to create a silhouette of the object.
Blur the silhouette (make sure that you have deselected Select > Deselect ): Filter > Blur > Gaussian Blur
Drag the silhouette layer below the layer with the object.
Rotate the silhouette in the general direction that the shadow will fall.
Add perspective to the shadow: Edit > Transform > Skew
Move shadow, if necessary, so that the base of the silhouette is visually attached to the base of the object.
Reduce opacity of the shadow by adjusting the opacity slider in the Layers Palette
Some additional painting or erasing may need to be done to make the shadow more realistic. Keep edges soft and adjust the opacity of the layer as needed. Sometimes you only need to add a soft, subtle shadow (indicating diffused light) to your image. This can be done by painting in a shadow with a soft-edged brush on a new layer below the object. Adjust the opacity of the layer as needed.
This is one approach (and there are many) to add snow to an image: