Instagram has some amazing filters. people love to use them all. sometimes you want to edit a picture without having to upload it on Instagram . its very easy. all you have to do is to publish a picture when airplane mode ON.
so first of all go to home page of your mobile phone and long press home button to get options like this
Turn On airplane mode like this
now go to settings and Turn On "Save Original Photos" option like this
now select a picture as you want to upload it on Instagram . use filters , hashtags as you wish. and publish that image on Instagram by clicking share option like this
that image will not be uploaded because airplane mode is ON. as you can see failed upload like this
but that image will be save in your gallery as you already ON save original pictures option. use that eidt image as you want.
in this way you can use Instagram as a photo editor.