Open the Instagram app or website
Find the photo you want to save
Tap the three dots on the post
Select Save if the option is available
Check your Saved posts in your profile
If you want the photo on your device, take a screenshot
Crop the screenshot to remove extra parts
If it is your own photo, open the post options and download your data or use the original file from your device
If the photo is from another account, ask the owner for permission before saving or using it