How to make your tumblr photo posts large again.
Add the following code to your theme's document.ready function, as well as into the callback for any ajax loading/infinite scrolling etc.
$(".post_media_photo_anchor").each(function(){ var $fullPhoto = $(this).data("big-photo"); $(this).find("img").attr("src", $fullPhoto); });
What this does is go through each photo anchor, take the data-big-photo attribute, store it as a variable to then quickly use it to replace the src attribute of the actual image (which, by default, is only 500px wide).
You might also need to force the size of the image using CSS, depending on your theme...
img.post_media_photo, .photopost img { display: block; max-width: none !important; width: 100% !important; height: auto !important; }
If you need help getting this set up, feel free to join my Discord Server and shoot me any questions. You can also catch me on Twitch from time to time.