Sure thing - no problem.
Are you moving the images from NGG back to the Media Library, or leaving them in the existing folder?
If you move them to the Media Library, make sure your
<img/> tags contain the
data-wp-pid=# attribute (so NGFB Open Graph+ can fetch the appropriate image size from the Media Library). When you add images from the Admin Editor, that attribute is added automatically, but you mentioned creating the
<img/> tag manually, so it's worth mentioning. ;-)
If you're keeping the images where they are, include accurate
height attributes so NGFB Open Graph+ can judge if the images are large enough to be used.
Let me know if you have any more questions.