Images in Maker
Edit theme → Theme settings → Images.

Product, collection, and article crops. Overlay titles and hover panes are in Product grid.
Image crop
- Product image size: Natural, Square, Landscape, or Portrait. This crop is for the product grid.
- Collection image size: collection lists and thumbnails.
- Article image size: blog cards.
Natural keeps each file’s own ratio. A fixed ratio makes overlay titles easier to place. Export sizes: What image sizes should I use?.
Shoot for the crop
Overlay titles are easier on a consistent ratio. Mixed lifestyle crops in a square grid will chop subjects. Natural is kinder to mixed photo sets.
Ask Sidekick 
Open Sidekick from the theme editor toolbar (top right, next to the device preview icon), or press ⌘. (Ctrl+. on Windows). Unsure whether Natural, Square, or Portrait crops will suit your product photography, or how consistent your existing photos actually are, describe your catalog. Maker's card titles often overlay the image, so the crop needs to leave room for type.
"My product photos are a mix of studio shots and lifestyle images, what Product image size gives overlay titles a clear area to sit in?"
It can help you reason through the trade-off before you commit the whole store to one crop, and point you to Shopify's image size guidance if you're about to reshoot.

Troubleshooting
- Images look cropped: Product image size, not a broken upload. Switch to Natural, or shoot for the ratio you chose.