The way to think about Images and other items on the site is that the site is broken down into 12 columns.
When you place items beside each other there is an automatic 12+12=24px margin between them.
Unless you manually pull on the item everything resizes to fit within those columns and margins. automatically.
In the case of Summary Blocks
This is 1 Column = 960px
Original Image: 960px wide x 600px high
Stays: 960px wide x 600px high
This is a 2 Column Break - 468 + 24 + 468 = 960px
Original Image: 960px wide x 600px high
Becomes: 468px wide x 293px high
Original Image: 960px wide x 600px high
Becomes: 468px wide x 293px high
This is a 3 Column Break - 304 + 24 + 304 +24 +304 = 960px
Original Image: 960px wide x 600px high
Becomes: 304px wide x 190px high
Original Image: 960px wide x 600px high
Becomes: 304px wide x 190px high
Original Image: 960px wide x 600px high
Becomes: 304px wide x 190px high
This is a 4 Column Break - 222 + 24 + 222 +24 +222 +24 +222 = 960px
Original Image: 960px wide x 600px high
Becomes: 222px wide x 139px high
Original Image: 960px wide x 600px high
Becomes: 222px wide x 139px high
Original Image: 960px wide x 600px high
Becomes: 222px wide x 139px high
Original Image: 960px wide x 600px high
Becomes: 222px wide x 139px high
This is a 7 + 5 Column Break - The Math Started getting rounded at this point.
Original Image: 960px wide x 600px high
Becomes: 548px wide x 343px high
This is a 7 + 5 Column Break - The Math Started getting rounded at this point.
Original Image: 960px wide x 600px high
Becomes: 386px wide x 241px high