Is there any way to work in custom field?

Of course. If you add images using custom fields you probably display them using get_post_meta() or some other custom fields related functions shipping with the plugin. All you need is to add rel=”lightbox” to an image link.

Something like that:
<a href="..." rel="lightbox"><img src="..."></a>

This way you can use it with literaly any image.

Thanks for the fast reply.
But I think you are talking about other plugin.

I’m talking about image-watermark plugin (not lightbox plugin) and
watermark does not appear when you uplaod image from custom field.

Please help me about this problem.

Oh, sorry ??

It doesn’t matter where you upload the file. If wordpress builtin upload script is used the watermark will be applied. Custom field is just where the file ID or path is saved.