Based on your reaction type, you should aim to use an image with the following size (or ratio).  Don't worry if your image is a different size, we will automatically resize the image for you.
(all dimensions in px)

Desktop Reactions:

Lightbox: 480 x 289

Side Bar (Left / Right): 350 x 207

Notification (Left / Right): 350 x 225

Tooltip: 120 x 133

Mobile Reactions:

Lightbox / 2-Step Lightbox: 337 x 200 (portrait) / 601 x 250 (landscape)

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