Thank you for your visit and for your kind comment.
There is a useful explanations behind that frame.
In fact the pictures I send on TN come from my website which has a black background. So that picture with the black background looks framed only by the small grey frame with my signature below.
Follow this link to understand what I mean :-)
It is then only for convenience for me that the black frame appears on TN.
Cheers and thanks for your pertinent comment :-)