Textures with transparent background can provide an inexhaustible source of possibilities for photomontages of any kind, from an iron fence to a curtain.
To get an image with alpha channel you need help from an editing software. When you open an image in any of these programs that has a one color background you can use the Magic Wand to select it. Use the Cut tool and save the image as a PNG or TIFF that are the only formats that will allow you an alpha transparency – background defined as transparent – in SketchUp.
I always tend to use textures when modeling can be too much time consuming or when I want to keep the face-count low. In this example I will use an iron gate to explain the steps that you have to follow.
The first step is to take or find a picture in a front elevation to avoid any picture distortions. Then cut the background with a photo editor and saved it in PNG/TIFF format.
In Sketchup create a new material using the new alpha texture and applied it on a face. You can see in this picture the interior of the wall denoting the transparency.
Erase and resize the area to have just one tiled texture with the appropriate dimensions and create a component. Once you finish the rest of the geometry edit the gate component and with the Shift+Erase tool hide the edges of the face.