Current US copyright law gives full copyright and usage rights to the creator of an image. Unless explicit permission is given, images may not be reused [except in very specific circumstances].
If you are looking for images to use in research projects your best bets for materials that you can use within copyright guidelines are:
Creative Commons Licensing
Creative Commons licensing provides a way for creators of images and other creative works to grant others permission to use their work in certain circumstances. There are different levels of permission that a creator can grant but the most commonly used are:
Creative Commons (CC) - Attribution [Author/Copyright Holder] (BY) Images and other creative works covered by this Creative Commons license may be reused in their entirety or may be mixed and reused to create derivative works as long as the original creator/copyright holder is credited. |
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Creative Commons (CC) - Attribution [Author/Copyright Holder] (BY) - NoDerivs (ND) Images and other creative works covered by this Creative Commons license may be reused in their entirety as long as the original creator/copyright holder is credited. |
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Creative Commons (CC) - Attribution [Author/Copyright Holder] (BY) - NonCommercial (NC) Images and other creative works covered by this Creative Commons license may be reused in their entirety or may be mixed and reused to create derivative works for non-commercial use as long as the original creator/copyright holder is credited. Educational uses such as teaching materials and projects created by students for classs and generally considered non-commercial. |
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Creative Commons (CC) - Attribution [Author/Copyright Holder] (BY) - NoDerivs (ND) Images and other creative works covered by this Creative Commons license may be reused in their entirety for non-commercial use as long as the original creator/copyright holder is credited. Educational uses such as teaching materials and projects created by students for class are generally considered non-commercial. |
Learn more about Creative Commons Licenses
Works in the Public Domain
Usually images produced by the US goverment are in the public domain and may be reused as long as proper credit is given.