Placeholder Media Generator.

Wordpress Plugin Docs
Adding placeholder images and videos to your wordpress site is simple using the following shortcodes. The highlighted items can be changed.

Create Image:
[tempimg]
Specify height width and text:
[tempimg height=500 width=500 text=text]

Create Video:
[tempvid]
Specify height width and length:
[tempvid height=500 width=500 length=10]

Download from wordpress.org