removing a solid color background from an image in HTML is possible using an SVG filter, which can be applied to HTML content.
i wouldn't recommend you actually use this method, removing the background in GIMP or photoshop or whatever is probably how you should solve it, but it is possible.
.demo_table {
background-color: lime;
}
.remove_white_bg {
filter: url(#remove_white);
}
<svg height="0" style="position: absolute">
<filter id="remove_white">
<feColorMatrix type="matrix" in="SourceGraphic"
values="1 0 0 0 0
0 1 0 0 0
0 0 1 0 0
-1 -1 -1 2 0" />
</filter>
</svg>
<table class="demo_table">
<tr><th>original image</th><th>same image + filter</th></tr>
<tr>
<td><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/01/Adaxial_side._Leaves_of_trees_in_autumn.jpg/136px-Adaxial_side._Leaves_of_trees_in_autumn.jpg" /></td>
<td><img class="remove_white_bg" src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/01/Adaxial_side._Leaves_of_trees_in_autumn.jpg/136px-Adaxial_side._Leaves_of_trees_in_autumn.jpg" /></td>
</tr>
</table>
(see here for more info on how <feColorMatrix>
works)