The law allows for the unlicensed use of a copyrighted image if it constitutes fair use, which courts evaluate on a case-by-case basis. (Even if it doesn’t qualify as fair use, a person is more likely to avoid a legal battle with the image owner if they give them proper credit.)
Courts evaluate fair use by looking at factors such as:
The purpose and character of the use: courts are more likely to consider educational or personal purposes as fair over commercial uses.
The nature of the copyrighted work: courts are more likely to protect creative works than factual ones.
The quantity and quality of the copyrighted work used: courts are more likely to support a small amount of use than a large amount.
The extent of harm to the owner’s market: courts consider whether the unlicensed use has (or may have) a negative impact on the copyright owner’s income.
Anyone who is unsure whether their use of a copyrighted image constitutes fair use should contact the image owner and ask for a Digital Image License.