I guess there are some photographers among the users here. I'm shooting a fair amount of pictures myself, and I use the 'raw' file format and process the images in Photoshop or Lightroom afterwards.

However, now I'm going to make a website for a painter. He sends me photos of his paintings, and many of those photos are in poor quality. he uses some low-res jpg.
I cannot recommend him to use the raw format, which is meant to be post-processed. If I start editing his photos, I may get it wrong, as I haven't seen the actual paintings. So what I would like to ask is, what format should I suggest that he uses? Would tiff be ok? Other suggestions?

Hi Inger
One question you may have to ask is he / she deliberately sending poor quality images because of copyright by displaying poor quality images some photographers artists do that to try and deter people from copying the images.
Just a thought

Jpg are fine as long as the photos haven't been diminished in quality. They will still be to big for website and need reducing.

I use jpg, we all use images which are too large. That slows the page.
I have started running them through:
https://tinyjpg.com/
Keith

I use the Image Compressor you can get from https://www.coffeecup.com/website-insight/

Thanks for your replies, guys! I was mainly thinking of displaying the images of the paintings as well as possible, so I didn't want to start off by using an image which might have been saved a couple of times over each other, each time reducing some jpg quality a bit further. I did not think about maybe he was reducing the quality on purpose, to protect his work against piracy, like Wayan mentioned. But I know this man, he is a very able painter, but he isn't really a great photographer. But I will discuss the matter with him.
Thanks for all your inputs.