When you take elements from one image and paste them into another to compose a new image, key things are required for the resulting image to look professional.
1. You need the element's perspective to be close to the background image. This means if the element you are pasting was taken with a very wide-angle lens, and the background of the image you are composing is taken with a telephoto lens, the perspectives won't be matched, and it just won't look right. Try to select images that are taken with a similar focal length.
2. If you paste an element that does not have the correct lighting or shadow, it will look like a sticker is pasted onto the picture; it won't look blended. So it is important to adjust the shadow to the direction of the strongest light source. Depix tools make it easy to add a ground shadow or a shadow on the wall and make lighting adjustments for tone on the image fragment to blend it with the background.