Embedding of art into .flac

I was certain I had done this previously, but it appears as if I did not. You can see in the image that the option to browse for an image is not available. I've searched 'embed flac' in the forums and found a few topics that make it seem like people are able to do this, but they were not describing the steps to actually embed the art.

If someone could point me in the right direction to do this, I would be very appreciative.

hmmm, it is nothing special. Open your files in the active window. On your left you see the artwork box (with I assume nothing in it). Find the artwork you want and copy it then right click on the artwork box and select either add cover or paste cover. And then be sure to select save files after this, otherwise the art you just added won't be saved.