The posts on the Tumblr dashboard can be of different types:
post with one image with link to post
post with one image with link to some arbitrary URL (typically external non-tumblr URL)
post with one image and no link
post with multiple images, each with direct link to high-res image
post with multiple images inter-spaced with text in-between, all images but the first with no link
NOW SUPPORTED (v1.2.0): post that acts as a link to an external URL and with an image as "thumbnail"
post with non-image content (e.g. movie or text)
post with ads
This script modifies all image posts (types 1 to 6) to link to their high-res version. (Currently this is 1280 for JPG and PNG and 540 for GIF - as of 2018-08-09 Tumblr seems to have cut off access to the raw version of images)
UPDATE 1.2.0 - 2018-10-27
fix for performance issue introduced with 1.1.0
NEW support for posts that act as links to an external URL. -> For these posts it does not make sense to completely replace the original link with the image link -> Instead, only the image will now link to its high-res version while the rest of the post still links to the original URL.
UPDATE 1.1.0 - 2018-10-25
display time-stamp of each post in the upper right corner -> For posts with "source app info" (e.g. "TumbleOn"), the time-stamp will replace this
UPDATE 1.0.1 - 2018-10-09
Requests to users of this script
Request #1: If any new possibility to access RAW images appears - please let me know
Request #2: If the time-stamp display doesn't seem to work correctly please let me know - the logic relies on several assumptions on how Tumblr posts are structured
The script is presented AS-IS with no guarantees - it works well for me, it might not for you...