On the web you should use one of
PNG - recommended for high colour or 265 colour images where you don't want artifacts
GIF - recommended for 256 colour images, also no artifacts or
JPG - recommended when small filesize is priority over image quality in high colour images.
Bmps are just big, especially for dialup users, too many people were posting them so now they aren't allowed, it's easy enough to save a compressed format like those above in any paint program, even newer versions of MS paint.
But from the jpg shot I think I know what you're talking about. when you import a 24 bit colour graphics into ags it gets reduced to 16 bit colour, 16 bit has less colours so the gradients don't look so smooth, there are some ways around it such as dithering an image down to 16 bit, not sure exactly how to do it as I never get this problem (must just be my style of drawing with less smooth gradients)
PNG - recommended for high colour or 265 colour images where you don't want artifacts
GIF - recommended for 256 colour images, also no artifacts or
JPG - recommended when small filesize is priority over image quality in high colour images.
Bmps are just big, especially for dialup users, too many people were posting them so now they aren't allowed, it's easy enough to save a compressed format like those above in any paint program, even newer versions of MS paint.
But from the jpg shot I think I know what you're talking about. when you import a 24 bit colour graphics into ags it gets reduced to 16 bit colour, 16 bit has less colours so the gradients don't look so smooth, there are some ways around it such as dithering an image down to 16 bit, not sure exactly how to do it as I never get this problem (must just be my style of drawing with less smooth gradients)