Only utility icons can be used with <lightning:buttonicon>. Alternatively, you can use any other SF provided icon using below mentioned way: <button name="lead" class="slds-button"> <span data-value="{!value}" onclick="{!c.controllerFunction}"> <lightning:icon iconName="standard:lead" size="small"/> </span> </button>
Now in above logic, if you replace the highlighted line with <img> tag as mentioned in the previously shared URL, you would be able to user your own icon.
<button name="lead" class="slds-button">
<span data-value="{!value}" onclick="{!c.controllerFunction}">
<lightning:icon iconName="standard:lead" size="small"/>
</span>
</button>
Now in above logic, if you replace the highlighted line with <img> tag as mentioned in the previously shared URL, you would be able to user your own icon.
https://developer.salesforce.com/docs/component-library/bundle/lightning:buttonIcon/documentation
Try the example as mentioned in it.
You can use like this.
<aura:application extends="force:slds">
<lightning:icon iconName="custom:custom20" />
</aura:application>
Aslo refer this link for more information
https://developer.salesforce.com/docs/component-library/bundle/lightning:icon/documentation
Kindly mark this as solved if the reply was helpful.
Thanks.