You can do this with the text widget. Depending on the size of the container of the sidebar, the following code should work well:
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<img class="alignleft" src="#" width="100" height="100" alt="" />
<div class="clear"></div>
Note: This solution assumes that you have the following css classes defined in your stylesheet:
img.alignleft {
margin: 0 7px 2px 0;
display: inline;
}
.clear{ clear:both; }
Whenever I need to put images in the sidebar, I use a similar solution.