Check whether JPEG Blobs are saved with full quality

This will be closed when we close #429 (closed)

capture_jpeg captures a JPEG, saves it to disk in tmp, returns the Blob with a link to the temp file, which we can then save with jpeg.save()

Need to test if the JPEG is being saved to tmp with some kind of quality factor limiting quality. We likely want Q=95, but defaults are often ~80