It would depend on the website but usually yes its ethical
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Answer:
On a Web page, we'll assume he'll have simple graphic elements like icons, or other simple low-resolution and a lower number of colors (256-), these are usually better saved in GIF format to take less space, just because of the smaller color map, but PNG could also do a great job and it offers transparency as well (like GIF does). For more complex elements (larger size and/o more colors like photos), the best format to save them is probably the PNG one. They will be compressed but still offer a great quality.
Explanation:
100 points yay
But I have only 50
