Check out our 'Image Sizing Guide':
We've compiled a list of suggested image sizes and dimensions to make updating photos on your site easier. Refer to this as you make updates to your site.
Blog Post Featured Image:
Minimum Size: 480x320px (3:2)
Resources Logos:
Recommended Size: 100x100px
Resources Featured Image:
Minimum Size: 480x320px (3:2)
Employer Profile Company Logo:
Minimum Width: 200px (no min length)
Employer Profile Page Header Image:
Minimum Size: 1220px (width) by 420px (height)
Recommended Size: 2000px (width) by 700px (height)
Static Career Community Content Block:
Recommended: Size: 400X150
User Profile Photos:
Recommended Size: 400X400
For the images in the staff page you should be sure to upload images with square dimensions.

Community Hero Images:
Aspect ratio: 3:1 Minimum size: 2100x700px
The most important thing to note here is the aspect ratio. If your image is larger than the minimum size requirement, but doesn't fit the aspect ratio, parts of your image will still be cropped in order to fit the frame.

Home Page Banner:
Recommended Size: 1600x460px

People Content Type Featured Image:
Minimum Size: 480x320px
Event Featured Image:
Minimum Size: 480x320px
Classes Featured Image:
Minimum Size: 480x320px
Organizations Logo:
Recommended Size: 400x400px
Organizations Header Image:
Minimum Size: 1200x400px
Recommended Size: 2100x700px
Experiences Logo:
Recommended Size: 400x400px
Experiences Header Image:
Minimum size: 1200x400px
Recommended Size: 2100x700px
Videos Thumbnail Image:
Recommended size: 800x450px (16:9)