This FAQ applies only if you are using the "Add image to post via imgbb.com" button to post images in your Individual User Gallery. It does not apply anywhere else! (Background: The upload plugin and the Gallery plugin do not work well together, necessitating the following procedure.)
[Click here for how to create an Individual User Gallery]
Here are the steps to follow:
In your gallery, click the Add Image button Click the Add image to post via imgbb.com button Browse to the image on your computer or drag-and-drop a file
At this point you have a string inserted in the comment field; something like this (click to view larger):
Copy the part of the string that is between "img" and "/img" (the highlighted part in the above image)
Paste it into the Image URL field
Delete the string that was placed in the Comment field
Note that imgbb might insert some advertising as well. Be sure to delete that.
It should now look something like this (click to view larger):
Enter a Title, any comments you want, and click the Add Image button.