I want to apply styles to the images of forums with a box. I have in the file. Css
as follows:
img.d {
border : 1px solid #ccc;
padding : 5px;
background : #fff;
}
If I put
[imgs=photo.jpg class="d"][/imgs][imgs=http://www.minibb.com/forums/img/p.gif][/imgs]
How I can do?
[imgs=https://www.minibb.com/forums/img/p.gif][/imgs]

You should do it using encode/decode functions, not via direct CSS.

I would ask at first - why would you need it at all?
Implementation method depends on the reason of it.

Tom is right, you must apply all stylings, modifying BB codes functions (bb_codes.php).
You can't put them like you mention above.

I need to put it so, not that it is imperative. But I want to add a forum section of a photo of the week. I think the design is much better with a border on the picture.

You can add this in your bb_default_style.css file:

.postedText img{border : 1px solid #ccc;padding :5px;background: #fff;}

Thank very much for your reply tom. Now is working fine.