Image resolution has several considerations:

Pixel Dimensions ( top )

Similar to centimetres, pixels are a unit of measurement roughly based on the individual dots that make up an image. The current "standard" for high quality images is 1920 pixels x 1080 pixels, otherwise known as high definition or HD.

When uploading images to the site, pay special attention to recommendations on what size in pixels the images should be. Large images will typically be 1920 x 1080, whilst smaller tiles might be 1/4 the size at 384 x 216. Thumbnail images might be as small as 192 x 108 pixels.

The reason size is important is because websites are designed to display content in different formats ranging from PCs, to tablets to smartphones. Putting a large image where a thumbnail is expected will result in a poor web page view.

You can use graphics programs to resize and crop larger images to be smaller. Free applications like Gimp or paid ones like Adobe Photoshop can do this.

Image Quality and Size ( top )

There is always a trade off between quality and size. For example, a crystal clear 1920 x 1080 image might be over 750Kb in size... far too large to quickly download on a smartphone on an expensive data plan.

Instead, use the above mentioned applications to reduce the quality of your images to be less than 250Kb ideally. In Photoshop, there is an menu option called "Export" which allows you to save an image in JPEG (.JPG) format. As you reduce the image quality slider bar you will often be able to preview the quality of the image in real-time.

Summary ( top )

Use graphics applications mentioned above to resize, crop and adjust quality so that your images are the right dimensions and size for the web site.