I created a plugin that will randomly pick an image from a category (or comma separated list of categories) and then output information assocated with that image. Some of the information that can be retrieved within a form are an <img /> tag for the large image or thumbnail, the author, the caption, height, width, image and thumbnail url, etc.

Here is the list of supported form tags:

<txp:mem_img />
<txp:mem_img_url />
<txp:mem_img_thumbnail />
<txp:mem_img_thumbnail_url />
<txp:mem_img_caption />
<txp:mem_img_alt />
<txp:mem_img_category />
<txp:mem_img_width />
<txp:mem_img_height />
<txp:mem_img_author />
<txp:mem_img_date />