Screenshot APIs

ApiFlash — A screenshot API based on Aws Lambda and Chrome. Handles full page, captures timing, and viewport dimensions.
microlink.io – It turns any website into data such as metatags normalization, beauty link previews, scraping capabilities, or screenshots as a service. 250 requests/day every day free.
ScreenshotAPI.net - Screenshot API uses a straightforward API call to generate screenshots of any website. Built to scale and hosted on Google Cloud. Offers 100 free screenshots per month.
screenshotlayer.com — Capture highly customizable snapshots of any website. Free 100 snapshots/month
screenshotmachine.com — Capture 100 snapshots/month, png, gif and jpg, including full-length captures, not only home page
PhantomJsCloud — Browser automation and page rendering. Free Tier offers up to 500 pages/day. Free Tier since 2017.
Webshrinker.com — Web Shrinker provides website screenshots and domain intelligence API services. Free 100 requests/month.
Httpic.com — Turn any website into jpg, png or pdf. Capture full-page screenshots, adjust the viewport, and inject custom code. Free tier at 150 images/month.
Screenshots — Your API for Screenshots. With highly customizable options for capture. Free 100 screenshots/month.