Choose image size for the job it must do

Choose image dimensions for the space the picture must fill, then adjust compression. Shrinking quality alone can leave a large file that looks worse than a properly sized export.

Find the destination's current requirements and consider the intended display, including higher-density screens where relevant. Keep an original copy before experimenting. Use a separate export and avoid repeatedly saving over the only full-quality version.

Compare at the viewing size

Make a small set of candidate exports and open them at the size the audience will see. Look at edges, text and smooth areas rather than judging only a tiny thumbnail. Check the file size alongside the picture. A difference that is invisible in the intended use may not justify a much larger download.

Photographs, diagrams and transparent graphics can suit different formats. Follow the receiving application's support requirements and test the result rather than assuming one format is best for everything. Preserve necessary accessibility text and credits in the publishing workflow.

Upload a test if the platform changes images after submission. Inspect that delivered version as well as the local file. Keep a note of settings that worked for this use. The aim is a clear image with an appropriate transfer size, not the smallest possible number at the expense of the information the picture is meant to convey.