You can attribute images in several ways, and the important thing is that they are attributed correctly.
Always check whether you are allowed to use images. Images that you find on Google Search are not all just free for use. Always go to the source of the image and check whether the person who posted it is happy for you to use it! Then make sure you mention the actual source (Google Images is not a source!).
When you upload the image to Moodle, it asks for Author and Licence. Make sure you change these to reflect the actual owner and licence of the image. Also make sure you repeat this information in the imagedescription. If you have done both of these steps, that is all that is needed.
You can put a note at the bottom of your page, or in a block, stating where you got the images (the original source, remember not Google Images), and what sort of licence the image is under.
You can put this information in a caption under your image.
For example, this image here says "No attribution required". This means you don't have to attribute the original source, however, you should still state under which licence this image is used so that people know that it is public domain, no attribution.
Image licence: CC0 Public Domain, no attribution required.
We have put the licence information in the image description, though the hover text (also called alt text) doesn't seem to work in a glossary. If you find that is the case where you have placed your image, it is best to also put the information in a caption (as above), or a side-block.