After conducting some research on the resize feature, it appears that it is still relatively new and not widely supported by all major browsers. Based on my findings, there currently isn't an established method for customizing this element.
If you're interested in learning more about the resize specification, you can visit the following page:
https://developer.mozilla.org/en-US/docs/Web/CSS/resize
Given the limitations, there are two potential options available, although neither is without drawbacks:
1) Consider using a background image. While this won't completely hide the resize icon, it will help to obscure it.
2) Another alternative is overlaying a div to contain your desired image with "pointer-events: none;" applied. This approach allows the resize icon to remain visible but can be concealed beneath an absolutely positioned div containing your image.
.custom-image{
background:pink; //you could set this background to your custom image.
height:7px;
width:7px;
position:absolute;
bottom:0px;
right:0px;
pointer-events: none;
}
I have made updates to your fiddle to provide a demonstration. DEMO