File size for images and photos is a very rough way to determine the quality an image. In the above image you can see the HB50 cupcakes image is a .jpg file and is 2MB in size. The JoggingShoes image is also a .jpg file and is 71KB in size. A KiloByte or KB is smaller, much smaller, than a MegaByte or MB. So the JoggingShoes image is smaller than the HB50 cupcakes one.
A Graphic Designer or Web Editor will want the larger size photo as this gives them a higher quality image which they can manipulate. On the flip side, a friend with a dreadful internet connection will not look forward to a big sized file clogging up their inbox.
As a website owner or editor you are going to create and use a lot of photos and images. The better quality the images are, the better your site will look. However your site will slow down if the files are too big. It is recommended to size your photos to the dimensions recommended by your site and to keep file size to under 100KB.
Is your image square or portrait or landscape? The video below explains the difference between these aspect ratios, why it matters and how to use the free, online tool croppio to crop your images to the correct aspect ratio.