Yup it's free. Additional pro features allow you to merge multiple data sources into one image, and view analytical data such as number of views / where your image is being viewed from. But, if you find all that you want is already available, then there's no need to get pro.
I'm expanding it with more data sources, and as you mentioned a Custom JSON Data Source. (You'll be able to enter your own URL, and rasterizer will pull a json from the URL)
We got in contact via discord, sharing different developer ideas. Our projects are similar, but our target audience differs.
Bruzu - You can call an API link to instantly generate an image, text data / image data can be swapped out on the fly.
Rasterizer - You design an image and then once saved, it provides you with a static URL you can share and this static image updates when your data source updates.
Also I've fixed the github data source, as he found it wasn't working properly.
What is this?
Rasterizer.io is an image generator that takes data from different API sources and puts them onto an image.
For example, you can tell it to pull data from your youtube channel.
Rasterizer will then fetch your subscriber count, video count, and view count.
You can then use the number of subscribers displayed as text.
Whenever your image is refreshed, the text will update to match your Youtube subs.
It's a bit of flexing, but in image format.
Where can you use this?
You can use your generated image as a forum signature, email signature, or as an image in your userpage. As long as the image is not cached, it will stay updated when it's refreshed.
Why did you make this?
I was inspired by Stackoverflow Flair ( https://stackoverflow.com/help/flair )
It generates an image showing how much reputation and medals you have.
But I found it too restrictive, you couldn't show data from somewhere else, move the text/images, or change the background.
How can I make my own image?
1. Go to Data Sources, this will present you with a bunch of different sources, choose a location and enter your username/id for that source.
2. Go to Images, and make a new image, this will bring you to the editor.
3. Click on the Link icon (top left in toolbar), this will create a new linked text. Look in the sidebar and cycle Data Field dropdown.
4. Save the image
You've now made a dynamic image. Whenever your data source updates, the linked text on your image will also update.