It is not acceptable to simply add "(c) national newspaper's name" as you are still using an image without permission. You can find out more about copyright and fair use for online images here.
My favourite source is Morgue File where photographers upload their images and you can use them freely. It's a great place to check first but the quality can vary as many amateur photographers share their pics but it can be a good place to find images of real people, not models. You don't have to create an account and can start downloading images without giving any private information.
At freeDigitalPhotos.net you do need to create an account but you then have access to a vast library of stock photos and illustrations. All are high quality but you can only get small sizes for free. You must add an attribution naming the image creator and an acknowledgement to FreeDigitalPhotos.net.
Free Range Stock has a lot of high quality images available. You need to create an account and you are encouraged to comment on the photo before downloading but it is totally free use. It is suggested that you should include a photo credit as a courtesy mentioning Free Range Stock and the photographer's name but it's not mandatory and photos can be used uncredited.
On Flickr photographers can choose whether to make their image available to licence or to hold onto to the full rights. The Creative Commons options are well worth knowing about as many will allow re-use but you must remember to check which option is offered and always add the correct attribution.
Wikimedia Commons is another good source to check for locations and historic images. Actually pretty much anything! Individuals upload the images so do check the reuse information under each image as Wikimedia is clear that it does not provide any warranty regarding the copyright status so be sensible and check other sources if unsure.
Stock.xchng has a large library and the quality of the images is generally very high. You need to set up an account and when you download an image you are asked to notify the image creator when using the photo for public work.
I can also recommend iPiccy which is a free online photo editor so you don't need to download any software to your computer to make changes to the images such as resizing, rotating and adding effects.
Do you use any other copyright free image sources? Do share with us below in the Comments. Thanks!