The Whitman Archive strives to get high resolution tiff images from repositories, though we typically present jpeg derivates on the site.  When transcribing tricky manuscripts, the higher quality images are useful to our staff for enlargement. We also use the tiffs for creating much higher quality than usual jpeg images used with our zoomify feature on selected poetry manuscripts. In some cases, we have not been able to obtain sufficiently high quality images to make the zoomify feature worthwhile.
 
Throughout the site we have gone ahead and posted lower quality images when that is all we can get--perhaps because the only surviving copy of a newspaper is in microfilm form or because a repository is for whatever reason unwilling to provide a high quality image.