If you are including an image, it is recommended that the resolution be as large as possible. This will help to ensure high quality, high definition video. The last thing you want in your video is a fuzzy image.
In addition to selecting a size of image that is of sufficient resolution to be included in a learning object, you'll also want to ensure that the image is licensed for use and that you attribute it correctly.
Open your browser and visit Google.com

Select on Images Tab.

- Select on the images tab to migrate from a regular web search to solely an image search.
Use the built-in filters to limit your search.

- Select on Search Tools to reveal advanced filter options.
- Select on Size.
- Select your preferred parameter.
NOTE: In addition to selecting a size of image that is of sufficient resolution to be included in a learning object, you'll also want to ensure that the image is licensed for use and that you attribute it correctly.