Gramblr is a simple tool that allows you to upload photos directly from Instagram to your PC directly on your PC.
All you have to do is sign in using your username and password to access your profile and then select the image you want to upload. You just can not upload anything: it should have a square image with a 640 x 640 pixels, thus standing by Instagram's regular upload parameter.
In his interface, Grambler himself offers a website that squares your image, even though you can do it with a photo-editing tool. Once your picture is ready in JPG format, simply press the upload button.
Then your caption should be added and if you upload it, your mobile version will have the same options: Share photos on Facebook or on Twitter.
There is no alternative to the effects, so you have to stay permanently for filter-free results, but still it is a good option to upload photos from your PC, because the Instagram web version does not allow this feature.