Hi MarcelElbers,
Thank you for your purchase.

Can you please send me a link of that page where you insert wpdatatables so we can take a look?

Hi MarcelElbers,

There is a conflict with css from other plugin and if you comment this then will be active css from the theme that also have same rule and causing this issue.

Just add this code in Custom wpDataTables CSS under the "Custom JS AND CSS" in main settings of wpdatatables.

table.wpDataTable td img {            
    max-width:none !important;
}

This will be affected on all tables, but if you want just for specific one then insert this code(change the color that you need) on page where is that table between the style tag.(<style>Code here</style>)

Hi MarcelElbers,

Sorry for late response. 

We are located in Serbia and our working time is from 10:00 to 17:00 CET. business days.

Sorry for that it is not related to you ("change the color") so do not pay attention to that. if you want just for specific one then insert this code 

table.wpDataTable td img {            
    max-width:none !important;
}

on page where is that table between the style tag.<style>Code here</style> like this:

<style>
table.wpDataTable td img {            
    max-width:none !important;
}
</style>

Hi Marcel,

You forgot to insert open style tag. Insert this on the page:

<style>
table.wpDataTable td img {            
    max-width:none !important;
}
</style>