Should I work for free?

This chart will help you to make a decision.

http://shouldiworkforfree.com/#no5

This cart is a copyrighted work by Jessica Hische 2011

Image Placeholder Services

Here I listed some of my favorite image placeholder services :

1. https://placekitten.com/ - all of your placeholders will be kittens! (Or if you like bears http://placebear.com/)
2. http://placehold.it/ - boring placeholders but your draft will be more professional without kittens. You can change format, color, text and size
3. http://fakeimg.pl/ - alternative to placehold.it
4. http://loremflickr.com/ - Random real photos with given sizes. You can give tags or you can get only black and white photos.
5. http://p-hold.com/ - This service has too many features for image placeholding.
6. http://dummyimage.com/ - alternative to placehold.it . Thi service has also an interactive placeholder url generator form
7. https://placeimg.com/ - You can select categories. 
8. http://lorempixel.com/ - This service is more popular among others (has no more features from  p-hold.com but faster). 

Others 

This second list also has many funny services. Have a look

• http://placebeard.it/ - Bearded pictures
• http://www.stevensegallery.com/ placeholder images of Steven Segal
• http://www.placecage.com - Nick Cage placeholders
• http://www.fillmurray.com/ -  Image holders filled with Bill Murray
• http://www.nicenicejpg.com/ only Vanilla Ice jpgs

Bonus

Http status code image holder service

http.cat