Sega has released to the public an entire act of Classic Sonic in Green Hill along with some high resolution screenshots. Click the thumbnails to see them in their 5K glory.
One thing interesting to note is that the number at the end of each of the filenames of these images are UNIX time stamps. 1492046832 for example is Thu, 13 Apr 2017 01:27:12 GMT or likely the time these screens were taken.