can i format an image in libre office draw to make it semi transparent
It depends in which format you save the image after processing. For example, JPEG has no alpha-channel; therefore the image will always be opaque.
Please, improve your question to give more information on what you intend to do with the image. Draw may not be the adequate tool because it is a graphical program, dealing with shapes. If you fundamentally want to manipulate image properties, an image processing application like free Gimp or proprietary PhotoShop are better suited to the task.
Don’t forget to mention OS name, exact LO version and the type of your images.
You can make an object semi-transparent, this includes jpg images. Select the image and, in the Sidebar > Properties > Image, you can adjust the slider to the desired transparency.
If you save the file as .odg the objects will keep their transparency but you cannot export the image as jpg with transparency as the format does not allow transparency.
If you export the page as pdf then the transparency will be kept.
You could export the image as png or as webp but there would be a large increase in file size.