You can upload a profile photo just for Micro.blog by clicking “Account” on the web. Look for the “Edit” link under your current profile photo. Or, if you’re currently signed in, click here to choose a new photo.
A square format image will likely work the best, but is not required, unless you are using Micro.blog to host your podcast. The Apple Podcasts Directory requires a profile image be 1400 x 1400 pixels.
Until you post a profile image, the default light gray circle will appear with your posts in the timeline. (If you have a Gravatar account that uses the same email address as your Micro.blog account, Micro.blog will use your Gravatar profile photo until you upload one to Micro.blog.)