I’ve had pretty good success with vectorizing raster images in Inkscape (IIRC it’s a feature called “trace bitmap”) and then doing some cleanup and adjustments.

I’ve had pretty good success with vectorizing raster images in Inkscape (IIRC it’s a feature called “trace bitmap”) and then doing some cleanup and adjustments. There is some manual work involved, but it really depends on the source. I was once given a small, low-resolution gif and was told that was the only copy of the logo for the government agency I was doing the work for. A few days later, I had a fully scalable SVG that became the agency’s official replacement of the logo. As an aside, Inkscape is a wonderful tool and I have used it to easily create complete icon sets (hundreds of images), which is extremely impressive for FOSS. It even has an API you can use for things like batch processing.