Crops are rectangular you cam mask to any shape. Pixels outside the shape will be mask off. Document are rectangular. Some File formats support transparence the image displayed for the document can be any shape. Jpeg doe not support transparency jpeg image will always be rectangular Shape layers can be filled witt color , gradient or a pattern and can have layer style effects added. image can be masked to any shape. A path you creat can be defined as a custume shape.
Use the rectangular Shape tool and drag out the rectangle.
Select the Pen tool, and hover over the end line untill you see a small + next to the cursor, and click to add a new point
Hold down the Ctrl key (Cmd on a Mac) and drag the new point to the left.
Hold down the Alt key, which will change the cursor and click on your new point.
With the Shape layer selected, open the Edit menu and click on Define Custom Shape.
Your new Shape will now appear in the Custom Shapes
You can give the Shape layer a flag distortion with Free Transform (Ctrl T or Cmd T). Start the FT process and click on the Warp icon (top right below). Then use the drop-down (top left) and select Flag. You can control the amount with the handle on the shape.
You can then save the same layer as a new custom shape, and give a different name.
Alternative method :
1. Use the shape tool to draw a rectangle
2. Change to the polygon tool - set sides to 3 and path options to subtract front shape
3. Draw the triangle and use the path selection tool (black arrow) to position it
The shape layer remains editable and you can therefore change the fill color in the options bar: