I recently started a Customise gift printing business in which people send me their photos to print on Mugs/pillows/frames etc for various occasions but I have my doubts about this business. So, I want to know with appropriate dalil whether it's earnings are Halal or Haram.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is nothing wrong with printing out photographs or visual images of animate beings via computers or other printing devices if there is a need for it, according to the preponderant opinion in this regard. This includes printing them for educational, awareness-raising, research purposes, or other legitimate and permissible purposes. If there is no need for it, then it is better to refrain from printing them even though it is not prohibited, but it is more prudent in terms of religious commitment.

Accordingly, if you can find another permissible line of work that does not involve doubtful matters, you should switch to it. But if you could not find one, then there is nothing wrong with continuing to do this work, Allah willing. But please note that it is impermissible to print photos of women who do not observe the Islamic Hijaab. The same ruling applies to the photos that one knows would be used for unlawful purposes and occasions that are not prescribed by the Sharee‘ah. It is impermissible to print them lest you would be helping the sinner in his sin and falsehood. Allah, The Exalted, Says (what means): {...but do not cooperate in sin and aggression...} [Quran 5:2]

Allah Knows best.