Position and scaling of the images is stored in the dxf file. If you switch on Draft mode, besides that text is simplified and hatch omitted, images are shown as an empty rectangle. Probably also when the image file is not found, but I haven't tested this.
The path to the image is written into the dxf file, as you can see when you check "Properties" of the image, but you can't edit it there. So if you use the dxf from a different pc or usb, the path is not correct anymore.
But if the image is in the same folder as the dxf, it is always found where ever it was when it was placed into the drawing. At least this is my experience. So it should suffice to move or copy the original image file to the same folder as the dxf file.