Grey artifacts on edges of photos

Hello everyone,

I have been building a very simple photography website which is basically 5 portfolios of my work. I used Metaslider slideshows to show between 10-20 shots per portfolio. My theme is Twenty Twenty-five 1.4, I have installed and am using the following plug-ins: GenerateBlocks, Akismet Anti-spam: Spam Protection 5.6, SeedProd 6.19.9, and Metaslider free. The gallery photos are 2000×1333 px and to keep it simple any shot outside of this aspect ratio has been padded with a white ground or bands to keep them to a 2:3 proportion and that size, the ground of the site is also white. The problem is where the white edge of a white bordered shot meets the white ground, I get a grey artifact, sometimes it is on the sides, one side or the bottom or top of a shot. This is not the case with all the shots and by nudging the styles I have managed to reduce the appearance of these, however there are still some that persist. I have looked on-line for code to add to Additional css, this code did not work and the explanation was that it was not specific enough in targeting the right elements. I added a custom class through the WordPress free website builder, once I located the class in the pages code, I realised that there are probably enough classes and ids to target the right elements without my custom class. The site is in maintenance mode and can only be seen by using the view page button in the site editor. I wondered if I was to upload the code concerning the slideshow could someone identify the elements that need targeting and how to go about writing the css to get rid of the grey lines. I see now that there are elements that were not addressed by the code I tried, for example looking I see there is a container for the slide show, this does not appear in my list view.

Thank you

Chris