To insert an image as the background in CSS, you can use the background-image property. Here's an example of how to do it:

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body {
  background-image: url("image.jpg");
  background-repeat: no-repeat;
  background-size: cover;
  background-position: center;
}

In the example above, image.jpg should be replaced with the actual path or URL of the image you want to use.

The background-image property sets the image to be used as the background, while background-repeat: no-repeat ensures that the image is not repeated. background-size: cover makes the image cover the entire background area, and background-position: center centers the image within the background.

You can adjust these properties according to your specific requirements.

To stop the background image from repeating, you can use the background-repeat CSS property and set its value to no-repeat. This will ensure that the background image appears only once and covers the entire screen. You can also use the background-size CSS property to make the image the size of the screen. Here's an example:

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body {
  background-image: url("your-image-url.jpg");
  background-repeat: no-repeat;
  background-size: cover;
}

In this example, the background image will not repeat and will cover the entire screen. You can replace "your-image-url.jpg" with the URL or file path to your own background image. This code can be used with HTML and CSS.

It's hard to say without more information, but it's possible that the background picture is being tiled or repeated. This means that the image is being duplicated to fit the size of the element it's applied to, which could be causing the doubling effect.

You can check if this is the case by inspecting the element's CSS styles. Look for a background-repeat property and check that it's set to "no-repeat" to prevent the tiling effect. If it's set to "repeat" or "repeat-x/repeat-y", change it to "no-repeat" to see if that solves the problem.

Here's an example of how to set the background-repeat property to "no-repeat" in CSS:

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element {
  background-image: url('path/to/image.jpg');
  background-repeat: no-repeat;
}

If this does not solve the problem, it may be helpful to seek additional help or provide more details about the issue.

In CSS, you can add a background image behind a container using the background-image property. Here is an example of how you can use this capability:

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.container {
  background-image: url(/background.jpg);
  background-repeat: no-repeat;

  width: 100%;
  height: 500px;

}

You can use the background-image CSS property to add a background image from a local file to an element (in this case the body):

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body { 
  background-image: url('./my-background-image.jpg');
}

You will also need to set the background-size, background-repeat, background-attachment, background-position and background-origin properties appropriately based on the style you wish to achieve.

For more information, please see MDN Documentation on the background-image CSS property.