When adding images to any email campaign, the image size is crucial. An image that is large in resolution will load slowly for every email recipient.
The resolution will delay the time it takes the email recipient's email to load. In some cases, when the image loads slowly, such as on a DSL network, the email recipient may choose not to view the email at all.
The size in width and height of an image are also important. If one uses a larger image than necessary the shape of an email may become distorted.
Mailchimp provides a video tutorial on how to size your image properly at:
3) Click on the link that reads 'Back to Files' in the upper left of the window.
4) Select new image.
(side note: Aviary can edit any image into any size for the website too)
6) Close Aviary and inspect image size, then change the width and height to the width and height that you wrote down in step 2.
7) Save changes.
You can also use CANVA to edit photos, which is an online app that allows you to crop and add text to images: