I taught a cookbook writing class a few weeks ago and the question about recipes and copyrights came up... it always does. I've also received quite a few emails asking the same question, so here are the facts about recipes and copyrights.
Recipes, for the most part, cannot be copyrighted because they contain a list of ingredients and lists aren't covered by copyright. What is copyrighted in a recipe is the cooking methodology (the directions, written in the cookbook author's style for preparing the recipe) and the headnotes (the little bite of information which is usually presented under the recipe title, but sometimes appears at the end of a recipe as a cooking note).
If you plan to fill your cookbook with a mix of original recipes, recipes you've found online, in magazines, in other cookbooks (after tweaking the recipe by perhaps changing a few ingredients or the spices to make the recipe uniquely your own and rewriting the methodology), this is pretty much okay. Depending on how much you've modified the recipe, you might want to credit the source where you found the recipe, noting that your recipe was inspired by or adapted from such-and-such a cookbook or magazine or online source.
A cookbook is (and should be) so much more than just recipes and cooking directions. Cookbook authors put themselves--their style and personality--into the pages. This comes through in the theme and story line of the cookbook, and in the way the directions are written and bites of information are shared.
If you'd like to include a recipe you've found in another cookbook, or from a website or foodie blog, in the same way it was published, write to ask permission to use the recipe in your cookbook. Never, ever, never copy a recipe verbatim. That's plagiarism and a copyright infringement. Always give credit where credit is due.
Add a dash of common sense and a pinch of courtesy in writing the recipes for your cookbook. Make your cookbook uniquely your own.