Board Thread:Support Requests - Getting Started/@comment-4594870-20140601130135/@comment-856287-20140601173433

I don't think you can do it normally with wiki markup, but there is an alternative here: Snippets/Setting Image Size by Percentage via CSS

Since you're placing images into table cells, you don't have to use a  tag. You can apply the "resize" class from the example to the table cell instead, and then the image inside should be selected for percentage sizing.