BC doesn't resize images. The layout draws its style from the stylesheet called style.css, found in root > css.
As you can see in the image below, each list item is set with the same witdh of 220 px in order to properly align with the template layout.
You can modify that value to accommodate bigger pictures but you'll have to pay extra care to not breaking the overall layout. An alternative would be indeed to shrink the images. See several articles as example:
- lookup max-width
Still, the best way to go about this, considering image quality, would be to just upload images of matching size.
Agree with Alex. The best option will be to resize the image before you upload them, as BC does not allow to resize it.
You can resize any image you upload im BC guys. In those cases yes the images are scaled in CSS (which is not great as your loading a full bigger image) and not a good method to suggest to people but under any image in the media manager you can click it and click resize.
IT is a bad resizer mind you an does not consider the image itself.
Also, if they are using BC to add the picture to a layout or templete, they can add the picture full size then right click (or ctrl click for mac) and select properties and edit the image size there without having to rezise the picture in file manager.