There are a number of ways to do it automatically via a browser extension or via a piece of downloaded software, but if you just want to grab one or two images from an Instagram feed, here's a way to do it manually. It's a little cumbersome but is almost always guaranteed to work. For this example, I shall use the Instagram feed of
Zahra, and the Google Chrome browser.
1. Go to the Instagram feed (e.g. instagram.com/zahraelommali) and scroll down until you see the image you want to capture.
2. Click on the image to get it to full size (e.g. instagram.com/p/xok1cJKJZ6/?modal=true)
3. Right-click on the image and choose "Inspect element" from the resulting context menu. You will be taken to a multipane code window.
4a. The pane you should concentrate on will have some lines of code already highlighted. In our example, the line will be:
<div class="iImage" style="background-image:url(http://scontent-b-iad.cdninstagram.com/hphotos-xaf1/t51.2885-15/10890973_645902538864976_128312721_n.jpg);" data-reactid=".6.0.1.0.1.0.0.0:$frame894126528058136186:0.0.$=1$image:0"></div>
4b. Alternatively, there should be a line or two above the already-highlighted one which contains similar-but-not-exactly-the-same code. In our example, that line will be:
<div autoplay="" src="http://scontent-b-iad.cdninstagram.com/hphotos-xaf1/t51.2885-15/10890973_645902538864976_128312721_n.jpg" class="lfFrame Frame Image" data-reactid=".6.0.1.0.1.0.0.0:$frame894126528058136186:0.0"></div>
5. In both cases, though, the part of the line we need to concentrate on starts with
http://scontent-b-iad.cdninstagram.com/
because that is the URL of the image we want to grab. You need to grab the URL between the parentheses (in step 4a), or the URL between the quotations marks following "src=" (in step 4b). The result will be the same:
http://scontent-b-iad.cdninstagram.com/hphotos-xaf1/t51.2885-15/10890973_645902538864976_128312721_n.jpg
The easiest way to do that is to hover over the URL (in step 4a); you will see a thumbnail image appear. If you click on that URL, the image will open in yet another multipane window. Right-click on that image, and choose "Open image in new tab" from the context menu. Or, if you grab the URL from step 4a or step 4b, you can open another tab, paste the URL in the address bar, and the image will appear there.
6. Right-click on the resulting image, choose "Save image as..." from the context menu, and that's that.
Hope this helps.