Apparently we used max-width (and max-height) on the image in a table ‘td’:

table td img {
max-height: 255px;
max-width: 345px;
}


This piece of code won’t get applied by IE8, so it seems…
But google found the solution right here, thanks to the forum user AsraiLight.
To let IE8 apply the max-width/max-height, you have to use a fixed table layout:

table{
table-layout: fixed;
}


This made it look like it is supposed to: