Hi there, I'm Matt Sergei (do call me Matt, please) and can help you with any multimedia files (images) handling in a web browser.
Yes, please provide more details. The graphics handling, display and exporting to PNG is not that hard, it's more about your customers actions on a web page. Would they be able to drop images on the "canvas", rotate them, stack one over other etc for the final image etc? Or what order of images is final or defined in a template etc)?
Otherwise I'm a webmaster and IT developer for 26 years, and graduated in digital image processing so know them very well. :-)
Looking forward to your reply, and hope you're safe,
Matt