The style applied to an Image in the style tag may not detect by the outlook app. SO the Image may appear in its original size in the outlook app.
For resolving the issue use the code below:
Code snippet:
In this code, the height and width are given outside the style tag for detecting in the Outlook app
<img alt="" data="customNew" src="${imageURL}" style="display: block; margin-left: auto; margin-right: auto; max-height: 64px; max-width: 64px;" width="64" height="64" />