The size of the images depends on the size of the browser window. If you change the size of the browser window, you will want to refresh or reload this program.
You should be able to browse for images in file folder. Some browsers allow dragging files to the browse button.
The resolution of today's digital camera significantly exceeds the typical monitor. For example, my camera takes pictures that are 4896 by 3672. But my monitor is only 1920 by 1080. Apts may attempt to resolve this in various ways. Some apts will automatically scale the picture to fit the monitor. Some apts have an additional option to enlarge a portion of the picture. This apt shows you both the scaled picture and an enlargement of a portion of the picture.
This apt is designed to be used with images that are "large" and is not appropriate for small images.
Images that have been rotated may show "unrotated". Apparently, some programs just add a "secret" marker to say the images is to be rotated without actually rotating the image. Unfortunately is program doesn't know that secret.
The p5.js file: Enlarge.pjs
James Brink, 5/12/2020