If you are using New Blogger and it's layouts, you can add photos or graphics to your sidebar using the add a gadget feature and selecting picture.
If you are using an old Blogger template, it's more complicated. You will have to create the image you want sized to fit in your sidebar. You will then have to upload it to a free hosting service such as Photobucket. Once you have done this, Photobucket will give you an address of where your picture is stored. It will start with http:
You will then use the below code:
<img src="the address given to you by Photobucket"/>
Change the text in red above to the address of your image.
Place the entire code above into your template in place of the below code:
<$BlogMemberProfile$>
Hope this helps!