Just to close the loop and answer my own question. Maybe others will benefit.
Mr. saguaro put me on the right course. Thanks. Then I spent some time thinking through this and learning through trial-and-error... Here is what worked for me in the end:
.blog .item .item-image {
height: 12em;
}
.blog .item .item-image img {
max-height: 100%;
max-width: 100%;
}
The idea was to set the container above the image (item-image) to the desired height, than force the image to fully expand or shrink into it. I am not 100% that this is the best way or even that it will work in all my cases, but so far so good.
Good luck.