I have an image having DPI value 100 but the publisher want it to be of atleast of 300 dpi...so what will be the solutions..please answer as soon as possible.
you just have to postprocess you images. On Windows OS you could use free IrfanView program (https://www.irfanview.com/main_download_engl.htm). From the menu choose Image->Resize/Resample and the dialog box will appear where will be the field with DPI. Just enter value 300 and hit OK button and thats it.
This of course will not change the quality of your pictures but only allows to meet publisher requirements.