When looking for images to include in a multimedia project, it is important to be aware of how resolution and compression can impact the aesthetic of your piece. Resolution is the number of pixels running horizontally and vertically in your image.
The standard resolution for a project that combines video, image and audio elements is HD (1920x1080). If you don't want your image to have artifacts, make sure the files you download are at least 1920 pixels x 1080 pixels. Using Advanced Search functions typically allow you to narrow your results by resolution.