Yes, you can allow only reading for a file or a folder. The simplest way is to create a folder on your computer (avoid Desktop), then place the image there and right click the folder. Go Share With > Specific People. Choose Everyone and then from the Permission column, select Read only, but keep in mind that this operation will allow them to copy the image to modify it on their computers. The file becomes read-only, which means only you have the power to apply changes.