From MongoDB's JSON Schema Examples Tutorial page:

JSON Schema is an IETF standard providing a format for what JSON data is required for a given application and how to interact with it. Applying such standards for a JSON document lets you enforce consistency and data validity across similar JSON data.

The purpose of a JSON Schema is to define the allowed property names and data types allowed to facilitate the validation of a given JSON object. This reminds me of TypeScript definitions, where type-checking happens by default after you've instantiated a given interface or class.

Pretty impressed by ImgIX's JSON format. Long story short, it provides a JSON metadata file for each resource you are serving via ImgIX (say, an image or a video) as in the example below just by appending fm=json to any image request.

For this image.

https://nono.imgix.net/img/u/profile-nono-ma.jpg

You'd load the JSON at.

https://nono.imgix.net/img/u/profile-nono-ma.jpg?fm=json

What's nice is that with the imgix.js JavaScript library you can fetch the JSON file for each picture and—before loading any image data—decide how to deliver the image. In this CodePen provided by ImgIX, they crop a set of images to fit a certain aspect ratio (which ends up saving data as they cropped bits of each image are never loaded) avoiding also having to play with image background CSS tricks in order to fit an image to a given aspect ratio (as the image already has it!).

{
    "Exif": {
        "PixelXDimension": 1500,
        "DateTimeDigitized": "2019:11:20 10:43:28",
        "PixelYDimension": 1500,
        "ColorSpace": 65535
    },
    "Orientation": 1,
    "Output": {},
    "Content-Type": "image\/jpeg",
    "JFIF": {
        "IsProgressive": true
    },
    "DPIWidth": 144,
    "Content-Length": "180595",
    "Depth": 8,
    "ColorModel": "RGB",
    "DPIHeight": 144,
    "TIFF": {
        "ResolutionUnit": 2,
        "DateTime": "2019:11:20 11:17:40",
        "Orientation": 1,
        "Software": "Adobe Photoshop CC 2019 (Macintosh)",
        "YResolution": 144,
        "XResolution": 144
    },
    "PixelWidth": 1500,
    "PixelHeight": 1500,
    "ProfileName": "Display"
}

And here's the JavaScript included in that CodePen that does all the magic.

// Demonstrate the use of the `fm=json` parameter to resize images
// to a certain aspect ratio, using ES6.

let ratio = 16 / 9;
let maxSize = 300;

let placeImages = function () {
    jQuery('.imgix-item').each((i, value) => {
        let $elem = jQuery(value);
        // We pull down the image specific by the 'data-src' attribute
        // of each .imgix-item, but append the "?fm=json" query string to it.
        // This instructs imgix to return the JSON Output Format instead of 
        // a manipulated image.
        let url = new imgix.URL($elem.attr('data-src'), { fm: "json" }).getUrl();

        jQuery.ajax(url).success((data) => {
            let newWidth, newHeight;

            // Next, we compute the new height/width params for 
            // each of our images.
            if (data.PixelHeight > data.PixelWidth) {
                newHeight = maxSize;
                newWidth = Math.ceil(newHeight / ratio);
            } else {
                newWidth = maxSize;
                newHeight = Math.ceil(newWidth / ratio);
            }

            // Now, we apply these to our actual images, setting the 'src'
            // attribute for the first time.
            $elem.get(0).src = new imgix.URL($elem.attr('data-src'), {
                w: newWidth,
                h: newHeight,
                fit: "crop"
            }).getUrl();
        })
    });
}

jQuery(document).ready(placeImages);