What type of disc to you need to copy data from your computer?

It is incorrect terminology to say you "download" pictures from a computer to a disk. When speaking of file replication from computer to removable disk, you say you "copy" the files, not "download".

Floppy disks were once popular for copying pictures from computer. Now we usually use writable or rewritable compact disks (CD-Rs and CD-RWs), DVDs (DVD-R and DVD-RW) and BluRay disks to copy files, including pictures, from computer.