I made a short tutorial on how to fix probably the most annoying problem any tumblr user will ever encounter.

First, start with the image or gif you want to use.

Save it to your computer.

Then you're going to click the text post button to create a new post.

Once you've done that, click the image icon and add your file.

Now we're going to fetch our HTML code, (select all & cut).

Return to the original post you wish to reblog. Paste the code in the HTML editor.

SAVE.

Ta-da! No more annoying gray boxes on your dashboard.