HTML image scaling based on window width?

[Mikey Z, Dr. Pixl]

I'm trying to learn HTML, and I want to add an image that I'll use as a divider. Is there a way to scale an image by a percent of the page width instead of pixel size?
"divider code"?

And the pixel size is going to vary, I'm trying to prepare for the quite likely situation where it's viewed on the wrong size of a device.

[AFRO NINJA]

No. files of any sort which are pictures or graphics cannot be moved by percentile. You can only set the size my dimension, (<img src="divider.jpg" alt="Divider" width="200" height="10">). Perhaps finding the right size of the pixels or pasting the divider code in the same line.