I need a bit of help please.
My web site here https://www.brian-lambert.co.uk/ uses a large amount of drawings. I was advised long ago (not by members of this community) not to upload the drawings as .JPGs as apparently they are slow in downloading and take up a lot more storage server space. So following that advice all my drawings are converted to GIF format and implanted into the web page. While they view OK, if the image is clicked on and then opened in a new tab it converts to an inverse image. See the two screen shots attached below.
My question to you is...Why are they being inverted and the background turning black and how can this be prevented?
Was the original advice sound in that .GIFs are better than .JPGs or should actually I use some other format?
Many thanks as always.

