Instagram still doesn’t offer an official method to post photos to the social network from your computer. That’s alright though because it’s still possible! Once you get this quick and easy process down, you’ll be glad you did. Most desktop browsers have a way of letting you change the “user agent” — the setting that tells a website what kind of device you’re on.
So when you’re on a laptop or desktop, you can trick a website like Instagram into showing you the mobile site version so it functions just like the app does. We’ll show you how to trick both the Apple Safari and Google Chrome desktop browsers into thinking you’re on a mobile device so you can use Instagram like you would on the mobile app to publish your content.
Watch this fast and helpful video first on how to do it for both Safari and Chrome browsers
Video by Sharon Profis, Jason Cipriani, Cnet.com
Safari Browser
Open Safari browser and click Safari > Preferences which will display the screen as seen below. Click Advanced tab and then checkmark the Show Develop Menu in the menu bar option.
Now open a new Safari window or tab and click on Develop > User Agent > Safari — iOS 12.1.3 — iPhone in the menu bar as seen in the image below.
Next, go to Instagram.com and sign into your account from that Safari browser window. At the bottom of the screen will be a + icon — tap it and select a photo from your computer to upload as seen in the image below. If the + doesn’t display on Instragram, refresh the page. After the photo is uploaded, you can still apply filters and edit the photo as you would in the Instagram app.
When you’re done, make sure you change your user agent back to the Default setting to avoid viewing all websites in their mobile state.
Chrome Browser
In Chrome, go to Instagram.com and sign in. Now right-click anywhere on the page then select “Inspect” from the list of options. Part of the site will be covered up with the Inspector tool, but we only really care about the small icon of a tablet and phone. 
It’s in the lower-left corner of the Inspector window currently but may have moved depending on when you read this. Click this icon and the page will change to a mobile view. You can select which mobile phone brand and/or model (i.e.) iPhone you want to view it in from the top navigation arrow, but they all mobile view the same. Now hard refresh the page and the + icon to create a post should show up at the bottom of the window on your Instagram as seen in the image above.
If the + icon doesn’t display on Instagram, hard refresh the page. If it still doesn’t show try running an Audit (found in the menu bar on the inspect page- see above video for this).
When you’re done, click on the tablet/phone icon again. Close the Inspector tool and refresh the website to go back to the desktop version.