Photoshop is an incredibly versatile tool that allows for a multitude of image editing techniques. One such technique is extending the background or the edges of an image, which can be particularly useful when creating banners, posters, or when needing to change the aspect ratio of an image without cropping out any essential elements. Here’s how you can extend images or backgrounds in Photoshop:

1. Open Your Image: Start by opening the image you wish to edit in Photoshop.

2. Unlock the Background Layer: By default, the opened image is locked as a background layer. To unlock it, simply click on the lock icon beside the background layer in the layers palette.

3. Select the Canvas Size Option: Go to ‘Image’ in the top menu, then select ‘Canvas Size’. You can also press ‘Alt+Ctrl+C’ on a Windows PC or ‘Option+Cmd+C’ on a Mac to access this option quickly.

4. Adjust Canvas Size: In the Canvas Size dialog box, you can specify the new dimensions for your canvas. To extend uniformly on all sides, make sure to click on the anchor grid so that all arrows are active. Then enter the values by which you want to increase the size of your canvas in either percentage or pixels.

5. Extend with Content-Aware Scale (Optional): If you’re intending to stretch a certain part of your picture such as a less detailed background, use Content-Aware Scale by going to ‘Edit’ and then choosing ‘Content-Aware Scale’. Dragging this will allow Photoshop to intelligently fill in areas with patterns from your image.

6. Use The Clone Stamp or Healing Brushes (For Detailed Edits): If your extension requires more attention to detail because it involves complex textures or patterns, consider using clone stamp or healing brush tools. These will help you manually sample and replicate parts of your image for a seamless extension.

7. Merge Layers (If Applicable): If you’ve used multiple layers to extend your image, ensure that you merge them down onto one single layer once you’re satisfied with your edits.

8. Save Your Extended Image: Finally, don’t forget to save your newly extended image. Go to ‘File’ and then ‘Save As’, choose your desired format and location, and click ‘Save’.

Using these steps in Photoshop allows anyone from beginner level editors to seasoned professionals to extend their images with ease, preserving important elements while adding necessary space for various formats and compositions.