When you shrink your screen to turn Instagram’s interface into a mobile interface, you can quickly force the ‘+’ icon to appear which on the app is used to upload photos. In turn, you can select media and upload it without having to use a phone or other smart device. Here’s a step-by-step guide.
1. Open Instagram on your browser
2. Click the RMB (Right Mouse Button) while the cursor is on a blank space in the screen
3. Select ‘Inspect’ or the alternative command in your language.
4. Select the ‘Toggle Device Toolbar’ option (highlighted in red in the image) until you get an interface which looks like the one on the app.
5. Now just refresh the page (shortcut for ‘Refresh’ is F5)
6. Finally, just point the cursor to the ‘+’ icon on the bottom (highlighted in red in the pic below, it’s actually the very same icon used for uploading via the app) and click on it
7. Select the image or video which you want to upload by using Mac or Windows file explorer
8. Use the editing interface to crop the image, apply filters, etc.
9. Post it!
Alternatively, you can upload posts on Instagram from computer with third party apps, find out more in full article here.