On the desktop version of Instagram, that menu button is on the bottom right. On Chrome, you'll find it in View > Developer > View Source. (Firefox, Microsoft Edge, and Safari also allow you to view source.)The text on this page is HTML, which tells the browser how to arrange the elements on the webpage for a viewer. It's not computer code, it's what's called markup, or formatting, basically. It's not hard to learn to read HTML — here's a good place to start. Use Control+F or Command+F and search for JPG. It's usually the first link. Copy the link starting with https.You can save or download the photo from here by right-clicking on the image and selecting Save Image As.... (The picture of my cat is a bit small, because it was uploaded years ago. Recent photos are often much larger.)