Please give more details before asking for help !
https://buddypress.org/support/topic/when-asking-for-support-2/
BP use the standart WP process to upload pictures. The default user avatar is set in the WP settings > discussion where you can choose between different avatar services. The default avatar shipped by BP is Mystery Man.
When a custom user avatar is uploaded by a member, the picture goes to wp-content/uploads/avatars/ into a folder named by the user ID. The original image is handled by the process to result in 2 different size, and BP rename each file to something unique with a MD5 name, and a human comprehensive name, such as c3f55cb7f3beaa22f7463132f5e0878d-bpfull.jpg and c3f55cb7f3beaa22f7463132f5e0878d-bpthumb.jpg
Internally BP use 3 default sizes for the user avatar: 50×50(small), 150×150(full) and 450×450 (max original file size).
These sizes can be changed. Read here how: https://buddypress.org/support/topic/avatar-sizes-in-1-7/
Each user can modify his profile and change his avatar so many times he want. The avatar upload process contains also an avatar cropper. The default cropping size is related to the avatar define “full”. By default it’s 150×150 and the original image is fixed to 450, even if it’s bigger on the user side.
Depending the placeholder of a profile avatar, those size are adapted to fit the template part fixed in the theme you use. On activity stream under bp-default theme, the avatar is 20×20, on members directory it’s 150×150, etc
The signup process is conditionned by registering. As long as a new user has not activated his account, he cannot upload or modify something, or even loggin to the site. That’s why there is no option for pics at this stage.
And yes, you can embed a profile pic into a sidebar or any other place. But this is only possible if you’re familiarized with BP and if you have some basic PHP knowledge.
