The issue has most likely been unrelated to info-beamer itself but instead was caused by local network policies. It’s working now.
While it’s true that JPG is a lossy image format, you have a lot of control over the quality/image size ratio. Anything encoded with the usual quality settings controls set to a value above 90% is probably not noticeably different to PNG. The downside with PNG is the often slower decoder on the Pi and the increased image size. It might be worth evaluating which format to use depending on the image content. If you have fine lines and high contrast content, PNG is probably better. For photo content, JPG most likely is.