Picture Clips from Google's Public Domain Books

From A Book of Cheerful Cats and Other Animated Animals (1903), showing a "Study of Hedgehog Stealing Apple".

Using Google Books' "Advanced Book Search", search with "Public domain only" and "Books" selected to narrow to whatever topic you want. Click on the search result to load the book into Google's reader. Scroll to the picture you want to copy and use the tool to create a box around the picture. After loading, a "Share a clip" dialogue box will appear. Copy the URL in the image field. When you post to Blogger.com, paste this URL into the "Or add an image from the Web" field to upload your clipped picture.

I always add the title with a link back to the book on Google to give credit where credit is due.