如何调整图像大小或作为NSAttributedString NSTextAttachment完成（或设置其初始大小）

I have a NSAttributedString to which I am adding a NSTextAttachment. The image is 50w by 50h but I'd like it to scale down to reflect the line height of the attributed string. I thought this would be done automatically but I guess not. I have looked at the UImage class reference but this image doesn't seem to be set in a UIImageView so no access to a frame property. Here's a screenshot of what I currently have:I have a NSAttributedString to which I am addin