Consumers are funny about mobile. On one hand, they spend more time on their smartphones and tablets now than ever. On the other hand, they still have reservations about making purchases from those devices.

The third annual UPS report on consumer shopping behavior, released this week, found that while more than half of consumers prefer online shopping, they aren't won over by the mobile shopping experience just yet.

If you're building a mobile shopping app, take note: Almost half of the consumers surveyed said they will forego making a purchase on their mobile device and use a PC instead because the product image isn’t large or clear enough.

Related: 7 Stats Show Mobile Marketing is Crucial for Your Business

About a third of the respondents said product information isn’t large enough on mobile shopping apps and 3 in 10 said comparing products was frustrating on a mobile device. Respondents were allowed to select more than one reason.

Consumers also reported being worried about the safety of giving out their credit-card information out through a mobile device. And about a quarter of respondents said that checking out through mobile is too annoying.

For the complete survey results on why ecommerce shoppers are still resistant to the m-commerce experience, check out the graph below.

Why Online Shoppers Still Don't Use Their Phones to Buy Things

Related: Mobile Phones Are Changing Retail. Here's How. (Infographic)