Images are usually copyrighted (even if you find them on the internet) and may be used for educational purposes including use in slides, on the OLE or elsewhere provided they are cited and serve an instructional purpose.
Using images in presentations or on the OLE
If you are delivering a lecture or seminar presentation, you may use any image to illustrate a point that you are making. You should always include an acknowledgement of the source of the image.
If you wish to use an image which does not illustrate a point in your teaching, you should only use an image where you have explicit permission for this sort of re-use.
Use low resolution images when uploading images to the OLE
The guidelines above are based on the legal exception of fair dealing with a work for the sole purpose of illustration for instruction. Further advice is available from the JISCLegal website (the site is now archived but the advice is still valid).