This issue just arose a couple of days ago. It's been a long, long time since I experienced this particular problem at WordPress. com. Side by side images set at same height display at different heights in page or post.
Example 1: The following two images are embedded in my leading post, http://songbook1.wordpress.com/2012/12/03/songbook-site-index/, each with the same height of 260 pixels.
<p style="text-align: center;"><img class="alignnone size-full wp-image-101220" title="1969-Poppy Family-Which Way You Goin' Billy-LP-1" alt="1969-Poppy Family-Which Way You Goin' Billy-LP-1" src="http://songbook1.files.wordpress.com/2012/12/1969-poppy-family-which-way-you-goin-billy-lp-1.jpg" height="260" width="260" /><img class="alignnone" title="Poppy Family-1" alt="Poppy Family-1" src="http://songbook1.files.wordpress.com/2012/12/poppy-family-1.jpg" height="260" width="214" /></p>
However, the left image displays about 20% larger than the right.
Thinking that the issue might be localized to that post, I made a test page:
Oddly enough, the reverse occurs in this case. The same two images are used and set at identical heights. But this time, the right image displays at about 15% larger than the left.
The blog I need help with is songbook1.wordpress.com.