The best way to fix the width and height of an image is to use an image editing software or the HTML attributes 'width' and 'height'.
In an image editing software, like Photoshop, you would edit the image by changing its pixel dimensions or by changing its resolution. For example, you could reduce the size of an image to 800 x 600 pixels or by setting it to 72 dpi (dots per inch).
In HTML, you can set the width and height of an image by adding the 'width' and 'height' attributes to the image tag. For example, if you wanted to set the image size to 300 x 250 pixels, you can use the following code:
<img src="file_name.jpg" width="300" height="250">
Using either approach, you can make sure that the image has a fixed width and height, which will make it much easier to control and manage.