If you are using Sharepoint 365:
According to Microsoft
In a recent update to Office 365 that is currently being deployed, the ability to automatically switch to new images is being deprecated for libraries that do not have a Content Delivery Network (CDN) enabled. This means that the AutoPlay functionality for existing websites will no longer function for Picture Library Slideshow web parts.
The full information from Microsoft can be found HereHere
To use the CDN together with the Picture Library Slideshow web part, your SharePoint Online tenant administrator must enable the CDN within your Office 365 tenancy.
You can find the steps to enable CDN within tenancy heresteps to enable CDN within tenancy here
But to help in case of link death here is the pertinent information
Using Office 365 CDN in SharePoint Online Here are the steps to get started with the Office 365 CDN.
Make sure that you are using the latest version of SharePoint Online Management Shell You can download SharePoint Online Management Shell from following link: https://www.microsoft.com/en-us/download/details.aspx?id=35588
Connect to your SharePoint Online tenant with PowerShell
Connect-SPOService -Url https://vesaj-admin.sharepoint.com
Get status of the CDN settings from tenant level
Get-SPOTenantCdnEnabled -CdnType Public / Private
Enable CDN in the tenant
Set-SPOTenantCdnEnabled -CdnType Public / Private ...
Public CDN enabled locations: */MASTERPAGE */STYLE LIBRARY
Disable CDN in the tenant
Set-SPOTenantCdnEnabled -CdnType Public / Private -Enable $false
Get default configuration of your public CDN settings
Get-SPOTenantCdnPolicies -CdnType Public ...
Key Value --- ----- IncludeFileExtensions CSS,EOT,GIF,ICO,JPEG,JPG,JS,MAP,PNG,SVG,TTF,WOFF ExcludeRestrictedSiteClassifications ExcludeIfNoScriptDisabled False
Add new CDN origin
Add-SPOTenantCdnOrigin -CdnType Public -OriginUrl sites/cdn/cdn ...
Public CDN enabled locations: */MASTERPAGE */STYLE LIBRARY SITES/CDN/CDN (configuration pending)
See the list of CDN origins
Get-SPOTenantCdnOrigins -CdnType Public ...
*/MASTERPAGE */STYLE LIBRARY SITES/CDN/CDN
Remove CDN origin
Remove-SPOTenantCdnOrigin -CdnType Public -OriginUrl sites/cdn/cdn ...
Public CDN enabled locations: */MASTERPAGE */STYLE LIBRARY
