The gallery is template based. Templates are located at:

Providers\HtmlEditorProviders\Fck\FCKTemplates

There are 3 template types: FlashBrowser, ImageBrowser, LinkBrowser

If you want to modify a template for the image browser named DEFAULT, go to the

Providers\HtmlEditorProviders\Fck\FCKTemplates\ImageBrowser\Default

folder and modify each Template.htm as you need.

Note that there is a master file to store general properties named: TemplateData.resx

That is a normal VS resource file and the width, height and other values are stored there (You can edit it with notepad or VS) (Just keep the utf-8 format).

Those templates are full localizable and you can see a sample of a localized template here:

Providers\HtmlEditorProviders\Fck\FCKTemplates\ImageBrowser\MoreInfo

Suggestion:

Try to build your own template (i.e. copy the default one into a new folder). This will prevent your customized data to be safe when upgrading the provider (Files will be replaced)