Here's a Wordpress plugin that you can install in your Wordpress blog which allows you to insert stock images directly to your post. I have been using this
stock images plugin for quite some time and it's very less buggy than the other plugins. It has got a couple of salient features:
(a)all of the images it finds are free and have a CC (creative commons) license
(b)Simply drag and drop the searched images from the list to your post. It sits right in the sidebar of the posts / pages edit screen, so you don't have to open up a new browser window to search for images for your post