UPDATE: blob issue updated, lowered bid.
Hi, my name is Matt Sergei (do call me Matt) and can help you with your image creation/conversion (26 years a webmaster and IT developer, multimedia pro and converting images with scripting and manually for 12+ years).
Yes, the tool of choice is ImageMagick, I have recently finished a project that converts (logo) images to SVG.
So the intent is to use command line version of PHP, right? OK, it will:
1. Retrieve the image from your function call.
2. Parse the JSON file, use the logo yet what does the template look like?
3. It will store the canvas (that ImageMagick uses) content to the blob, no issues here - though this works if the canvas is displayed on the web page. I'll have to check if this works "headless" e.g. not in a web browser. UPDATE: well, no issues here, image binary data can be managed.
Looking forward to receive more details and hope you're safe,
Matt