You can use CSS’s `background-color` and `rgba()` properties to make a background semi-transparent. Here’s an example:
```
div {
background-color: rgba(255, 255, 255, 0.5); /* Where 255, 255, 255 is white and 0.5 is the opacity (50% transparency) */
}
```
In the `rgba()` property, the first three numbers correspond to the red, green, and blue color channels, and the last number is the alpha channel which controls the opacity. 0 represents fully transparent and 1 represents fully opaque.
Remember to apply the transparent background to a div, not to an image, because images don’t have a background color. You then place your image inside this div.
For example:
```
and in your css:
```
.transparent-bg {
background-color: rgba(255, 255, 255, 0.5); /* semi-transparent white */
padding: 10px;
}
.transparent-bg img {
display: block;
}
```
