If you have a large amount of images in your SharePoint site - it may be hard to find what you're looking for without thumbnail images. SharePoint can generate and show thumbnail images - but it isn't setup to do so by default. You have to add a thumbnail column to your site. Here's how.
- Go to your SharePoint library.
- Click on the Add Column button at the top of the list of files (as shown in the screenshot below):
- Choose Picture for the column type.
- Give the column a name (Thumbnail is recommended for the name)
- Click Save when done.
Images (and other files that SharePoint can generate thumbnails for) will show a thumbnail image. If you have multiple SharePoint sites - this has to be done on each site you want thumbnail images to show up on.